Born in the year 162 CE--before Buddhism was popular in China--he pursued studies of China's classics while working as a bean-curd seller.  Even today, people in this profession consider him to be their patron.  He was said to have a prodigious memory, and was able to recite extraordinarily long passages of the classics.

Unfortunately, he became embroiled in controversy and had to flee into the mountains.  It seems a magistrate had forced a poor girl to become a concubine.  Coming to her aid, Guan Yu ended up slaying the magistrate.  While fleeing to the next province, Guan Yu stopped to wash in a stream, where he saw his reflection and discovered that his face had taken on a reddish tint.  This happenstance, which provided him with a more-than-adequate disguise, accounts for the fact that many representations of Guan Yu show him with a deep red face (though the one at Hsi Lai Temple does not).

Having become an "outlaw," Guan Yu was soon joined by two "sworn brothers," Zhang Fei with a black face, and Liu Bei, with a white.  These three colors--red, black, and white--are often found together in Hindu and Buddhist teachings.  For example, the Vedas teach of three gunas or "qualities," which, when in balance, make up a whole human being.  The white guna signifies sattva or peace, harmony, etc.; red signifies rajas, which is passion, activity, etc.; and black signifies tamas or inertia, negativity, etc.  So Guan Yu has, through too much passion and activity, gotten himself into trouble; by allying himself with power forces representing the other two gunas, he brings himself into balance.

At any rate, together these three had many dashing adventures, which are detailed in the stories known as "The Romance of the Three Kingdoms."  Finally, he was put to death by an enemy leader in the year 219.  Buddhist legend says that the night he died, his ghost appeared to a Buddhist monk, requesting to be instructed in the Dharma.

The story picks up again a few hundred years later.  It seems that Ch'ih Yi (or Chih-I), the founder of Tiantai Buddhism, needed to build a new monastery on Jade Mountain.  Unfortunately, the land he had was not level enough for building.  As he sat meditating, who should appear but the ghost of Guan Yu.  He promised to make the site buildable, and is said to have done so in one night!  So Master Ch'ih Yi instructed Guan Yu further in Buddhism, and Guan Yu received the Five Precepts from him.  For this he is called "Sangharama," which is a Sanskrit designation for the place the Sangha (monastic community) lives.  He is, then, especially associated with monks, nuns, and their dwelling places; this is the aspect I have emphasized in the Intention section.

Through the years, various emperors have honored and elevated him, generally under the name "Kuan Di" ("Di" means "god" or "emperor," a title granted him during the Ming Dynasty).  He is popular as a God of War and Prosperity, and is honored by Taoists and Buddhists alike.

You can read the Buddhist form of his "history" in my Ascent pages.  More on his adventures can be found in this encyclopedia article on The Romance of the Three Kingdoms, and at this Romance-related biography page.  On related pages you can find biographies of his companions Liu Bei and Zhang Fei (often depicted with him at temples), and more on the Romance.