Mahar is a skeletal monk who acts as Zaheer's bodyguard. Mechanically, he is a leadership cohort. Mahar was brought back from the dead by the psychopomp spirit Ankou.
As well as wearing full-body wraps to hide his skeletal nature, Mahar normally wears a Hat of Disguise, causing him to appear as a living human.
Personality wise, Mahar has a sarcastic demeanour, especially toward Zaheer. Despite this, he is clearly devoted to his charge, practically having a panic attack when he goes missing in the Feywild.
It is implied that he is working for the Shepherds as atonement for some kind of sin committed during his mortal life, although the exact nature of said sin is unclear.