A man of many names, including Starman, Thom Kallor has been a part of numerous super teams, including the Justice Society of America and the Legion of Superheroes. The latter has been teased in Supergirl, which recently left CBS to air its second season as a
part of The CW's ever-expanding Arrowverse.
Why Thom could work is simple: he has the ability to send people to alternate dimensions via his suit, which is actually a map of the Multiverse, a concept that was explored to great extent in season 2 of The Flash. This power could easily tie into the storyline for the sophomore year of Legends.
Even if they went with his non-reality transporting powers, Thom Kallor would be a tremendous character to show in battle, as he has the ability to alter the mass and density of a person. Either way, this JSA veteran could be a lot of fun to have around.