A brahmin foremost in Mithilā in his knowledge of the Vedas.
On hearing of the Buddha at the age of one hundred and twenty, he sent his pupil Uttara to discover if the Buddha had on his body the marks of a Mahāpurisa. Uttara therefore visited the Buddha and, having seen the thirty two marks, resolved to observe the Buddha in his every posture and, to this end, followed him about for seven months. He then returned to Brahmāyu and told him of the result of his investigations. Brahmāyu folded his palms reverently and uttered the praises of the Buddha. Soon after, the Buddha came to Mithilā and took up his residence in the Makhādeva ambavana. Brahmāyu, having sent a messenger to announce his arrival, visited the Buddha.
It is said that all those present rose to greet him, but Brahmāyu signed to them to be seated. He satisfied any remaining doubts he had as to the marks on the Buddha's body and then proceeded to ask him questions on various topics. At the end of the discussion he fell at the Buddha's feet, stroking them and proclaiming his name. The Buddha asked him to compose himself, and preached to him on "progressive" discourse. Brahmāyu invited the Buddha and his monks to his house, where he entertained them for a week. His death occurred not long after, and the Buddha, when told of it, said that Brahmāyu had become an Anāgāmī (M.ii.133ff). Brahmāyu's salutation of the Buddha is described as panipāta. ItvA.177.