Skanda, also known as Wei Tuo, is a Mahayana Bodhisattva regarded as a devoted guardian of Buddhist monasteries who guards the Buddhist teachings. His Chinese name is 護法韋馱尊天菩薩 (Hufa Weituo Zuntian Pusa), meaning "Honored Dharma Protector Skanda Bodhisattva", because he is the leader of the twenty-four celestial guardian deities mentioned in the Golden Light Sutra(金光明經).
In Chinese temples, Skanda faces the statue of the Buddha in the main shrine. In others, he is on the far right of the main shrine, whereas on the left is his counterpart, Sangharama (personified as the historical general Guan Yu). In Chinese sutras, his image is found at the end of the sutra because of his vow to protect and preserve the teachings.
According to legends, Skanda was the son of a virtuous king who had complete faith in Buddha's teachings. When the Buddha entered into nirvana (涅槃), the Buddha instructed Skanda to guard the Dharma. It was his duty to protect members of the sangha(僧伽) when they are disturbed by Mara(魔), the tempter, and also to resolve conflicts amongst members of the sangha. A few days after the Buddha's passing and cremation, evil demons robbed his relics. Skanda's vow of protecting the faith and Dharma was proven when he managed to defeat the evil demons and returned the relics.
Skanda is described as a young man fully clad in the armor and headgear of a Chinese general, and is usually leaning on a vajra staff (金剛杵). Some suggest that Skanda may have come from Hinduism as the war deity Kartikeya / Muruga (Tamil), who bears the title Skanda. Others point out that Skanda might also be a manifestation of Vajrapani(金剛手菩薩), a Bodhisattva who bears some relations to Skanda because they both wield vajras as weapons, are portrayed with flaming halos, and are both heavenly protectors of Buddhism. Although Skanda is only a deva (天人), he is very often addressed as a Bodhisattva.
There are 2 stories about how Skanda becomes a guardian of Buddhism.
The first story is related with Miao Shan(妙善公主). When Avalokitesvara Bodhisattva was reincarnated as the princess Miao Shan, Skanda (known as Wei Tuo in this story) was one of her cruel father's generals. He loved Miao Shan but realized he could not possibly be a proper partner to her, since she was a pure person. However, Wei Tuo was inspired by Miao Shan's kindness so he decided to stay faithful and devoted to Miao Shan, even if she wasn't his wife. The two decided to escape from Miao Shan's father, and the general helped Miao Shan build a temple and a kingdom of her own. Soon however, the cruel king found them and killed them both. The general, because of his devotion to Miao Shan, Avalokitesvara Bodhisattva, transformed into a Bodhisattva himself, who vowed to always serve and protect Avalokitesvara Bodhisattva. His appearance as a Chinese general is the direct forbear to his connection with Miao Shan.
Another story says that Miao Shan was told to be killed by her grandmother. Her grandmother forced Miao Shan to commit suicide by leaping into the sea because she was thought to have been an incarnation of a demon, when in fact she was not. The emperor told a loyal soldier named Luo Ping to pretend to throw Miao Shan to the ocean, but he actually brought her to her mother's village. Years passed, an evil fish demon came. A disloyal soldier named Huo Yi, was sent from the fish demon to kill Miao Shan. The fish demon wanted revenge on Miao Shan because she was the incarnation of Ci Hang Da Shi(慈航真人), a Buddhist deva that put her in a lotus pond. Huo Yi and his troops went to the village where Miao Shan and Wei Tuo lived and fought. Huo Yi's son killed Wei Tuo. After Miao Shan became the Bodhisattva Avalokitesvara, she made Skanda a Bodhisattva guardian because he took care of Miao Shan and loved her as a sister.
According to the lunar calendar, his birthday is at the 3rd day of the 6th lunar month.