They are both exiled Sleestaks and the only members of a criminal band led by Shung. They are entirely submitted to their leader and always try to please him, but Shung rarely appreciates their efforts. Shung always sends them in the jungle to perform the dirty work.
Nim is the smarter of the two, while Keeg is the idiot of the band. Nevertheless, Keeg is a very strong fighter and also an excellent tracker.