The descriptive name of a brahmin who visited the Buddha at the Ajapālanigrodha seven days after his Enlightenment and asked him questions regarding the true brahmin. The Buddha explained the matter, but made no impression on him (Vin.i.2; see also Ud.i.4; UdA.54; cf. Mtu.iii.325).
Buddhaghosa explains that the brahmin was a ditthamangalika, filled with haughtiness and wrath, and went about uttering the sound "hu-hum." hence his name.