War Hawk

Batman Beyond
In the Batman Beyond two-part "The Call", War Hawk disliked Batman (Terry McGinnis) because he was recruited into the Justice League by Superman without his consent as well as the rest of the JLU. War Hawk started to respect Batman after their battle against Starro. War Hawk even appeared in the animated series' related comics where he and the Justice League help Batman against the second Matter Master, Jokerz, and Black Light.

Justice League Unlimited
In the season one finale "The Once and Future Thing, Part II: Time Warped", War Hawk met the modern day Green Lantern (John Stewart), the original Batman (Bruce Wayne), and Wonder Woman after they were sent to the future by a time traveller known as Chronos (Dave Clinton). War Hawk, Static, Future Bruce Wayne, and Batman II allied with those heroes from the past in dealing with Chronos and the Jokerz. War Hawk revealed to John that he is Rex Stewart, the son of John and Hawk Girl which surprised John meaning he wouldn't be with Vixen in the future. Regardless of that known fact, John protected his son when he was in a death battle against the Jokerz. After the cyclical causality erased memories of the team-up from the future JLUers and Wonder Woman, only John and Batman retained knowledge of War Hawk existing. John decided to keep this information a secret from Hawk Girl which Batman agreed.

In the third season episode "Ancient History", John told Hawk Girl that she is to become the mother of his child and stayed with Vixen despite his love for Hawk Girl.

In the Justice League Beyond comic books, John decided to be with Hawk Girl after Vixen was murdered by Shadow Thief and he was removed from the Green Lantern Corps for contributing to Shadow Thief's demise that would eventually happen. John and Hawk Girl quit the Justice League and got married. The two of them had a son together and raised him in Africa.