An arhat (this is Pali; the Sanskrit is arahant) is, in simplest terms, a follower of the Buddha who has attained her or his own Enlightenment.  In Southern Buddhism, this was the Ideal.  There is only one Buddha in any given Age, according to the Southerners, and the best that anyone else can hope for is Arhatship.  This is attained through intense meditation, which leads to Wisdom.  When we come to Mahayana Buddhism, a shift in the Ideal takes place.  Those who consider Wisdom and the attainment of Enlightenment for themselves to be the goal, and who pursue this without thought for the Enlightenment of others, are deemed selfish or, at the least, truncated somehow.  In one scheme, portrayed in the Lankavatara Sutra, there are Ten Stages on the Way to Bodhisattvahood.  There is a danger at Stage Six of becoming "enchanted by the bliss of the Samadhis" and thus "pass to their Nirvana" without completing the Way--thus being Arhats, not Bodhisattvas.

However, both Mahayana and Southern Buddhism recognize that the Path of the Arhat is essential; even Bodhisattvas must go through these first six stages, cultivating Wisdom, before moving on to Stages Seven, Eight, Nine, and Ten. So the Arhats have been a common motif in Chinese art from the earliest days.

The Chinese call these eighteen the "Lohan."  This is derived from "a-lo-han," a phonetic approximation to the Sanskrit "Arahant."  In Japan, the abbreviated "lohan" has become "rakkan."  Read more about them on this page from my Aki Meguri.

The history of the Arhats in Chinese art is tortuous, to say the least.  The first paintings in China of groups of lohans (Arhats) involved only sixteen Arhats; and even this was an increase from an original four!

The Ekottara-agama, among others, records a tradition that the Buddha appointed four Arhats-the "Four Great Sravakas" Mahakasyapa, Kundopadhaniya, Pindola, and Rahula-to remain in the world and not achieve final Nirvana until Maitreya, the next Buddha, arrived.  They were to guard the Dharma (much like the Temple Guardians we have already met).  A later work, the Mahayanavataraka-sastra, then expands the list to sixteen, eliminating Mahakasyapa and Kundopadhaniya, but retaining Pindola, and Rahula as well as fourteen other, unnamed, Arhats.  These were subsequently identified in a Chinese work, the Ta-a-lo-han-Nan-ti-mi-to-lo-so-shuo-fa-chu-chi, known as the Fa-chu-chi for short.

Now we're up to sixteen (and sixteen is the standard number in Tibet and Japan).  But where did the other two come from?  They are in fact very late.  Even in the seventeenth century sets of sixteen could still be found in China (they are still common in Tibet, and sometimes Japan).  The late date of the two additions is attested to by the fact that they keep changing names!  This, at least, is consistent: in almost every case, the additions are "[Name] with a Dragon" and "[Name] with a Tiger."  Sometimes they are "taming" or "subduing" the beast, sometimes "riding" it, but they are virtually always in its company.

Why did the artists expand the number of Arhats to eighteen?  There is no one answer, but there have been many suggestions.  One of the most interesting came from nineteenth-century scholar and traveler T. Watters.  He suggests that the number eighteen came from a political model:  In the year 621 Emperor T'ai Tsung selected eighteen Imperial Scholars who came to be known as the "Eighteen Cabinet Ministers."  Watters suggests that this may have stimulated the artists to "enhance" the number.  The Eighteen Cabinet Ministers served in groups of three; the Arhats are often portrayed in groups of three.  Portraits were made of the Eighteen Cabinet Ministers, with brief biographies appended; the same was done for the Arhats.  And so on.  Others have suggested that the number eighteen reflects Taoist influence, it being two nines, and nine being auspicious as three threes; many important numbers in Chinese lore are multiples of nine, such as 72, 108, 180, and 360.

Aside from the question of why two Arhats were added, there are also minor confusions in the main sixteen: sometimes it is Ajita riding a deer, and sometimes Pindola.  If Ajita is on the deer, then Pindola has long eyebrows, and vice versa.

The group of Arhats is often called "The Assembly at Vulture Peak."  In Mahayana tradition, the Buddha often met on Mount Gridhrakrta in central India--the peak of which is shaped like a vulture's head--with an astonishing assembly of natural and supernatural beings: "monks and arhats, Boddhisattvas of foreign lands, incalculable numbers of gods, dragons, yaksas, asuras, and other sentient beings."  Here he would deliver his sermons, later to become sutras.  So the Arhats were key attendants of the Buddha's teachings, and later came to be seen as guardians.

As with the Christian apostles, some Arhats have extensive legends, and some have only  minor ones.  I will give brief stories on each one here.  The order here is the traditional one.

• Pindola, The Arhat with Long Eyebrows (1): (Also called Pindola the Bharadvaja)  This Pindola is leader of the Arhats.  Sometimes shown with long eyebrows, he and Ajita are sometimes switched, so he is sometimes shown riding a deer.  The name "Pindola the Bharadvaja" is sometimes used because one of the candidates for inclusion as a 17th or 18th Arhat is a second Pindola.  The eyebrows indicate longevity, signifying seniority and, thus, leadership.  Another legend says that he was born with these eyebrows!  It seems he had been a monk in a previous life who tried--but failed--to gain Enlightenment.  He hung on to life, striving for attainment, for such a long time that finally all that was left were the two long eyebrows! (Image at Buddhanet)
• Kanakavatsa, The Jolly Arhat (2): (Also called Kanaka the Vatsa)  He was a great debater and orator.  When seekers asked what happiness was, he would say it came from the five senses; but when asked about Bliss he said it came, not from the outside, but from the inside.  Not being subject to changes on the outside, it could then be sustained indefinitely.  He is sometimes seen banging cymbals in his joy.  (Image at Buddhanet)
• Kanakabharavaja, The Alms Holding Arhat (3): (Also called Kanaka the Bharadvaja)  He was famous for begging with his bowl-and his eyes-upraised, accepting gifts without shame.  He is often portrayed with one foot in the air; this may be the position of "royal ease" (one raised knee), but looks more like he is dancing like Shiva!  In any case, he represents one who can receive gifts graciously. (Image at Buddhanet)
• Subinda, The Pagoda Holding Arhat (4): (Also called Nandimitra)  This was the last disciple to meet the Buddha before his death; afterward, he carried a pagoda to remind him of the Buddha's earthly presence.  The scholar Watters says that he is sometimes portrayed with an alms bowl and an incense burner next to him; he holds a scroll in his left hand, and is snapping the fingers of his right.  Watters says, "This gesture is indicative of the rapidity with which he attained spiritual insight."  Given how briefly he knew the Buddha, it may also signify his understanding of the impermanence of things. (Image at Buddhanet)
• Nakula, The Silently Seated Arhat (5): (Also called Vakula)  It is said that Nakula was a former warrior with immense strength; all of the violence of his former life led to deep concentration as a monk.  Nevertheless, even in meditation, he exuded strength.  He is sometimes portrayed holding a rosary, with a small boy by his side.  Other portrayals show him with a mongoose, or a three-toed frog; these are perhaps due to associations with other folk figures. (Image at Buddhanet)
• Bhadra, The Arhat Who Crossed the River (6): (Also called Bodhidruma)  Little is known of Bhadra, but much can be said about the attribute of "crossing the river."  From the crossing of the Jordan to the crossing of the Rubicon; from dreams of "the other shore," to the silly joke about the chicken and the road, to today's New Age life-after-life show "Crossing Over": This image is widely used for attainment of "the other side," which symbolizes some exalted spiritual state.  The Pope is called the "Supreme Pontiff," meaning bridge-builder; the Jain leaders were called "Tirthankara," meaning ford-maker.  Almost every religion uses this imagery, and here it is embodied in the slim little figure of Bhadra. (Image at Buddhanet)
• Kalika, The Dust Cleaning Arhat (7): He is sometimes a dust-cleaner; in other depictions he is an elephant tamer.  Can these be reconciled? Easily: The mind is the elephant, and needs to be tamed; the mind is dusty, and needs to be cleaned.  These are both traditional Buddhist metaphors for the process and goal of spiritual practice.  Both processes require patience, concentration, and diligence.  Kalika represents these. (Image at Buddhanet)
• Vajraputra, The Persuading Arhat (8): This is another tough character to track down.  In some iconography, he is a "persuader" who convinced Ananda that both practice and understanding were necessary to achieve Wisdom; in other traditions, he is a "persuader" who tames lions!  Having been a lion-killer before becoming a monk, he was later joined by a lion cub who seemed grateful that he had given up his former profession.  So he is often portrayed with a lion by his side. (Image at Buddhanet)
• Jivaka, The Heart Exposing Arhat (9): (Also called Gobaka)  Oh, to have the heart of the Buddha!  Jivaka was a crown prince, meant to become king.  But he wanted to be a monk, and attain Enlightenment.  So he went to his second brother and said, "I relinquish the throne, and I will go off to be a monk."  His brother, distrustful, thought it best to eliminate him immediately, lest he come back later with an army and stage a coup.  "No need," he said, "I have the Buddha in my heart."  And in proof, he opened his garments, revealing the image we see at the Temple. (Image at Buddhanet)
• Panthaka, The Arhat with Stretched Arms (10): (Also called Maha-Panthaka, Great Panthaka, or Pantha the Elder)  His name, like his younger brother Culapanthaka's ("Little Panthaka") means "born on the road," and legend says that the brothers were born while their mother was traveling.  Others believe the name signifies that they are "on the path" of Buddhism.  This elder Panthaka is often considered to have had magical powers; others ascribe to him a leadership role in the early Sangha, and some even say he was a Prince.  He is sometimes seen with raised hands indicating that he has just come out of meditation. (Image at Buddhanet)
• Rahula, The Arhat in Deep Concentration (11): This is the Buddha's son (and one of the original "Four Great Sravakas").  His father left home to seek Enlightenment the day Rahula was born; his name means "fetters," perhaps suggesting that his father saw him as a bond to the householder's life.  As a young boy, Rahula sought out his father and asked for his inheritance; the Buddha taught him the Path to Enlightenment.  His gentle appearance here betokens his youth in comparison with the other Arhats. (Image at Buddhanet)
• Nagasena, The Ear Cleaning Arhat (12): The cleaning (or scratching) of his ear signifies that Nagasena ("Dragon Army") was anxious to hear everything correctly.  He has been identified with the great scholar Nagasena, who answered King Menander's questions in the famous early Buddhist dialogue The Questions of King Milinda.  If so, his careful listening paid off, as King Menander threw at him some of the toughest possible questions, and he answered them thoroughly.  (Image at Buddhanet)
• Angaja, The Arhat with a Sack (13): (Also called Angida)  Because of the sack, he has sometimes been confused with Maitreya Bodhisattva, and portrayed as fat and jolly.  I have also heard that Maitreya did not take good things out of his sack, but put evil things in.  This may be due to confusion with Angaja, who was a snake-catcher by trade.  He would catch snakes in his sack, de-fang them, and release them-exchanging bad for good.  This kindness allowed him to achieve Enlightenment. (Image at Buddhanet)
• Vanavasin, The Arhat Under the Banana Tree (14): (Also called Vanavasa)  Legend says he was born under a banana tree, or that he was born during a heavy downpour when the banana trees were making a lot of noise.  In a homely imitation of the Buddha, he sat under a banana tree where he gained Enlightenment.  He is sometimes shown seated on a banana leaf. (Image at Buddhanet)
• Ajita, The Arhat Riding a Deer (15): (Also called Asita)  As mentioned above, he is sometimes confused with Pindola.  This comes from a legend that he (or Pindola?) had once left the service of a king and snuck off to become a monk.  After his Enlightenment, he rode back into the place (presumably from the mountains) on a deer, was immediately recognized by the guards, and was ushered into the king's presence, where he taught him the Dharma.  The king turned the throne over to his son and followed the Arhat out to become a monk.  (Image at Buddhanet)
• Cudapanthaka, The Door Watching Arhat (16): (Also called Culapanthaka, or Pantha the Younger)  This is the younger brother of Panthaka above; his name means "Little Panthaka," or Road-born.  There are two famous stories about him.  One is that he was slow-witted, and unable to learn even a single verse.  But the Buddha, using skillful means, taught him to sweep (in some versions, to wipe) and repeat a simple verse, such as "Sweeping broom," to focus his mind.  This simple method led him to Enlightenment.  Another story says that he used to knock roughly on people's doors to beg for food.  Once, he knocked on an old, rotten door, and it fell to pieces!  So the Buddha gave him a ringed staff (like that held by Bhadra next to him) and told him to pound the ground with it, instead of pounding on the door with his fist.  Through this (and the sweeping association) he came to be thought of as one who guards the doors of the senses, letting only pure things in. (Image at Buddhanet)
• Maitreya, The Tiger Taming Arhat (17 or 18):  This is one of our "guest" Arhats.  His identity as Maitreya is something of a problem.  Remember that, originally, the Arhats were to remain "on duty" guarding the Dharma until Maitreya came.  Well, if Maitreya is one of them, then how…?  Anyway, for Maitreya's story, refer back to the section entitled "In the Hall of the Bodhisattvas."  The tiger here represents the passions; one story of the tiger-tamer (attributed to the second Pindola--remember, the name is not as important here as the attribute) says that there had been a tiger harassing a town; when the Tiger-Taming Arhat arrived in the area, he suggested feeding the tiger to prevent its depredations.  Naturally, the food given was all vegetarian, and the tiger thus became tame!  (Image at Buddhanet)
• Mahakassapa, The Dragon Subduing Arhat (17 or 18): (Also called Kasyapa)  This is our second "guest" Arhat, who could be designated "X, The Dragon Subduing Arhat."  That he is subduing a dragon--symbol of our deepest inner motivations--is more important than his name, since that changes.  However, that he is sometimes the Great Kasyapa, first of the original "Four Great Sravakas" assigned by the Buddha to stay and guard the Dharma, is very interesting indeed.  I do not know how he came to be "restored," but here he is.  He is best known for the Buddha's famous "Flower Sermon."  It is said that on that occasion, the Buddha simply held up a flower, and said nothing.  Only Kasyapa signified-by a wordless look-that he understood the Buddha's point, that the Truth is beyond words.  Some trace the Zen/Ch'an lineage back to this moment. (Image at Buddhanet)