The Time Trapper was the central figure in the world-shaking Crisis On Infinite Earths. In that epic, he set in motion events which would kill Supergirl, Flash II (Barry Allen), and retroactively destroy all the various multiple-Earths. In the end, however, he was defeated, in large part by the Legion of Super-Heroes.
Unfortunately, the Time Trapper was not content to disappear and lick his wounds. Instead, he planned a crafty revenge against the three original Legionnaires: Cosmic Boy, Lightning Lad, and Saturn Girl. Saturn Girl was now married to Lightning Lad, and the couple had a small baby named Graym. The Time Trapper kidnapped Graym, and plotted to exploit Lightning Lad’s well-hidden insecurity to ultimately destroy them all.