An incarnation of शिव . The ब्रह्माण्ड पुराण contains the following story about it.

When the हिमालय and मैनाक mountains once began a very intense तपस् , the देवस् and ऋषिस् fearing great ruin to the world in case the mountains got salvation, sought शिव 's protection and prayed for a solution for the problem. So शिव , in the guise of a ब्रह्मिन् named साधु , went to the mountains, spoke to them condemning शिव and thus made them retract from their devotion to शिव .