This article contains plot details from the latest book.
Opher is one of Tam's bodyguards. He is a dwarf. Opher was first mentioned in Book 8.5: Unlocked in Tam's registry file, in the category called Bodyguards. There, it was mentioned that Tam Dai Song has two bodyguards, one of which is Opher. Opher remains primarily underground and has not shared anything about himself with Tam.
The name Opher is Old English for "Riverbank."