Gondorian Renegades are the soldiers of Gondor who have been swayed to the side of the Dark Lord, Sauron, and 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 or NPC will be attacked by the Renegade using whatever weapon in their possession.
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.