First of all, yes, we're doing a listicle in two parts because The Legion of Super Heroes is that deep.
If comic-book superteams were Disney characters, the Legion of Super Heroes would be Daisy Duck; everybody has heard of them, but they never really take center stage.
For those who need the origin story, the Legion first appeared in 1958, in Adventure Comics #247, published by DC Comics. Some 1,000 years in the future (always relative to whatever time they were published in), they are a group of super-powered teenagers (later adults) from various worlds of the United Planets, dedicated to keeping peace and doing good. Their original origin had Superboy, legendary hero of the 20th century, as the inspiration for the team. Superboy joined in their first appearance and served as the lead character for the first two decades of stories. Throughout their 58-year history, Legion stories have delivered teen angst, allegories for political unrest and universal equality, space (and soap) opera, epic time-travel sagas, superheroics and straight-up, sophisticated sci-fi.
If they are known for anything, it's the frequent use of “Boy” “Girl,” “Lad” and “Lass” in its members' codenames (even into their adulthood and despite the fact that no one is Scottish), and for their multiple retcons (as of this writing, their origin has been rebooted six times).
This all said, we present to you our ranking of every single member ever, from least to most important. We here at Blastr are nothing if not completists, so a few disclaimers are necessary.
Disclaimer #1: Not counted are people who joined in speculative futures (sorry, Hate Face and Leeta-87). We’re only going for full-blown, Legion fight ring/belt wearer, even if it was brief. Years indicate when they joined, or when we learned they joined (lots of stuff happens off-screen).
Disclaimer #2: We are covering every incarnation of the Legion in comics. Reboot, Threeboot. Everything.
Disclaimer #3: While everything is subjective, rankings were determined by overall impact to the team, the comics and the mythology.