Fisk is a Blackguard, and former training of new inductees. After the disappearance of Commander Ironfist, Fisk reluctantly took over commander of the unit.
Fisk is a short but muscle-bound man with a shaved head. While training Blackguard hopefuls, he wore the standard Blackguard uniform but with a sleeveless shirt, which showed his massive biceps.
Early in the series, Fisk was a pawn of Andross Guile, who blackmailed him with exposing that his lover, Lytos, was a fellow Blackguard, and a eunuch.
This was a potent threat; if Andross had released this information, not only would having a lover who was a fellow Blackguard likely have resulted in Fisk being expelled from the Blackguard and ostracized, but he would have been ostracized even further for said Blackguard being a eunuch, a taboo in the Satrapies.
The one task that Andross wished of Fisk in return for not revealing the secret was to ensure that Kip did not make it into the Blackguard. When this failed (due to the intervention of Kip's teammate Cruxer,) Andross said that Fisk still owed him. However, Andross was never able to collect this time.
After the death of Lytos, Fisk went to the White (it is not specified if it was Orea Pullawr or Karris Guile, but due to the gap in time between Lytos' death and Orea's death, after which Karris was chosen to be the new White, likely Orea,) and confessed everything, removing the possibility of Andross blackmailing him for anything else.