Mahāsthāmaprāpta 大勢至

‘He who has obtained Great Power’, the name of an important mythical Bodhisattva. He is especially popular in east Asian Buddhism and is believed to open people's eyes to the need to strive for awakening (bodhi). Mahāsthāmaprāpta is mentioned at an early date in Mahāyāna works such as the Lotus Sūtra, and is often paired with Avalokiteśvara and depicted together with the latter flanking Śākyamuni or Amitābha in the form of a trinity. Iconographically, he is white in colour and is depicted holding an unopened lotus bud in his hand; sometimes he is also shown in east Asian art with a pagoda in his hair.  

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

【梵】mahāsthāmaprāptaḥ
【梵】महास्थामप्राप्तः【中】大勢至
【藏】mthu chen thob

Mahāvyutpatti - DDBC version