In Vajrayana Buddhism, Vajrabhairava, also known as Yamantaka, is
(1) a wrathful, buffalo-headed meditational deity (Tib: yi-dam) of the Highest Yoga Tantra class and/or (2) a dharma protector. Vajrabhairava is one of the principal three meditational deities of the Gelug school (Tib: gsang bde ‘jigs gsum; the others are Chakrasamvara and Guhyasamaja).
He is also one of the main yidams in the Sakya school where he comes in a variety of appearances (with different mandalas). In both schools Vajrabhairava is seen as the wrathful manifestation of Manjushri, the buddha of wisdom. In the other schools of Tibetan Buddhsim Yamantaka seems to be mostly revered as a protector. The (mostly secret and arcane) practices there involve different activities for various purposes. There are also some Yamantaka terma revelations in the Nyingma and Kagyu schools. From amongst the many lineages of practice to enter Tibet the main transmissions of Vajrabhairava were those of the two translators Ra Lotsawa and Mal Lotsawa. Although practiced early on in Tibet by the Sakya and Kagyu Traditions, it was Tsongkapa, founder of the Gelug Tradition, who instituted Vajrabhairava as the principal Gelugpa meditation practice.