Hayagriva

Hayagriva (Skt., Tib. Tadrin, lit. “horse-necked one“) is the manifestation of the wrathful form of
Loving Eyes (Chenrezig).

He is often depicted as being red with one face, two arms and two legs, a horse head above his head, as a warrior with roaring mouth, snake ornaments and a sword in his right hand.

His special ability is to cure diseases, especially skin diseases even as serious as leprosy, which is said to be caused by nagas.

Hayagriva has different forms according to different Buddhist traditions. The first one who installed the practice on him was Guru Rinpoche in the late 8th century.

In the 11th century Atisha practiced on Hayagriva as his main yidam. In his tradition Hayagriva appeared red colored, with two arms. 
The special practice on Hayagriva was passed on from Atisha through one of his students to Gampopa, who gave it to the 1st Karmapa. The practice belongs to one of the five sets of the five
deity practices of Düsum Kyenpa (the other four are Chakrasamvara, Vajravarahi, Hevajra and Tara). The 6th Karmapa later composed the sadhanas for the puja.