Alex Summers

Season One
Scott mentions him throughout the season.He is never mentioned again after that season,except for his flashback in Season Three

Season Three
In 1985,He,Sean Cassidy,Hank McCoy and CIA agent Moria MagTaggert join Charles Xavier and Erik Lehsnherr into having a team with Xavier's foster sister,Raven.Erik betrays them.Summers,Cassidy,MacTaggert and McCoy stay with Xavier though.