Monarch's future reign had been erased). Following this, both Matthew Ryders joined the Linear Men, a group that contained time-traveling beings who protected the time stream, with the powerless Ryder eventually become the team's leader. Despite the Linear Men's policy of non-intervention in the timeline – to the point that Waverider, was discouraged from preventing Superman's death during his first battle with Doomsday – Waverider came to Superman's aid when he discovered that Doomsday had returned to life and was now working with the Cyborg Superman. Recognizing the danger of Doomsday's existence, Waverider showed Superman a detailed vision of the past to explain the circumstances of Doomsday's origin as a genetically engineered being capable of evolving to overcome anything that proved capable of killing him. Waverider also discovered that Doomsday's hatred of Superman was due to Doomsday's traumatic origins on Krypton leaving him with a deeply rooted hatred of Kryptonians. The two heroes seemingly defeated the monster by taking him to the end of time, where the imprisoned Doomsday was destroyed by entropy as the universe itself collapsed. Later, during Zero Hour, Waverider was killed by Extant, who had evolved from Monarch. His alternate self, Matthew Ryder, was still alive, and was shortly thereafter contacted by Metron. Metron told Matthew that he had to become Waverider, and that he was the only one who could use time travel to save the universe. Matthew was then transformed into a new version of Waverider, and took the role his previous self did: helping a select group of heroes defeat Extant and Parallax's effort to recreate time the way that Extant and Parallax wanted it by triggering their own Big Bang with the aid of Damage. Death Junior and Georgia, two descendants of the villain Doctor Sivana, rebuilt their father's sphere of Suspendium which let them travel in time. Although they were able to open a gateway in the past, they ultimately had to stop their experiment. Right before shutting down the machine, they saw Waverider in the timestream but failed to recognize him. Later, Waverider was seen talking with the dying Time Commander, one of the former time-traveling villains who Waverider had tried to recruit in his efforts to save the timeline. Skeets, infected and controlled by Mister Mind, then arrived and killed the Time Commander. He then asked Waverider where and "when" Rip Hunter was in the time stream. When Waverider