Gondorian Renegades are the soldiers of Gondor who have become corrupted by the ways of the Dark Lord, Sauron, and have defected from their home country. They are loyal to the Eye, more specifically Umbar, and not the Steward of Gondor.
As with all Umbar units, these units won't attack any player with an alignment that's positive or neutral with Near Harad, as Umbar is a sub-faction of Near Harad. If the player or NPC approaching them isn't friendly with Umbar, then the player of NPC will be attacked by the Renegade using whatever weapon the soldier's holding.
Gondorian Renegades are capable of occasionally spawning in Umbar invasions. They are capable of spawning in Umbar too, but only on very rare occasions; finding one can be extremely difficult, bordering on impossible. The chance of finding one in an invasion is a rough chance of 1 in 3 invasions.
These units can be hired similarly to Shieldmaidens of Rohan. If right clicked by a player they will send the player to kill Gondorians. When the player turns in the quest they will receive both a reward and the Gondorian Renegade as a unit.