Chameleon Boy

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2984 - Reep Daggle is born on Durla, the son of one of the planet's religious leaders.
2989 - 5-year-old Reep runs away from his home planet, determined to break their cycle of isolationism & paranoia.
2991 - 7-year-old Reep joins the Legion of Super-Heroes in their first recruitment drive.
2996 - 12-year-old Reep's father passes & he is found by the rulers of Durla who demand that he takes his father's place.  He wins his independence, beginning a movement among the Durlan people to explore outside their planet, forever branding himself an outcast.
3000 - 16-year-old Reep is among the Legion members stranded in a distant Galaxy.  He becomes a public figure speaking for interplanetary relations after the Legion of Super-Heroes disbands.  He gains many enemies and beings inflitrating the groups that oppose him.
3005 - 21-year-old Reep discovers the Dominators infiltration of Earth.  He goes to Querl Dox to reform the Legion of Super-Heroes and stop them.
3006 - 23-year old Reep returns to Durla to speak out against isolationism.
Chameleon Boy is absolutely a marquee member of the Legion.  So much so, that when the animated Superman series made a episode featuring a three-person Legion team, he was the only non-founding member they used.  He was the very first member of the team that was deliberately depicted as being non human.  He has a pretty classic look, with giant spock-elf ears and his trademark antenna, although it's understood that this is just a look he's affecting, that Durlans are actually really weird and alien looking.

It's worth pointing out that Reep is the only member of the Legion that we allowed to maintain his original origin.  He has his shapeshifting powers because ALL Durlans have them.  This is because the character already has something in his story making him unique; He's speaking out against his people's isolationism.  The Durlans are actually a pretty well used alien species... of course there's the Durlan, a mysterious mentor character for Vril Dox who clearly has seen some stuff, but there was also a major invasion of Earth by the Durlans that happened in China as part of the backstory for Grant Morrisons' Great Ten.  They're a mysterious alien entity even in the distant future of the Legion, which totally makes the idea of Reep being a lone voice of compassion among his people makes him wonderfully unique.

Reep is the source of a LOT of the really super weird stuff that happened over the years in the Legion.  There's his pet Proty who looked... well... I'll let you google him and figure it out yourself.  We left the bulk of that out and focused his story on his relationship with his people, and we're left with a really fascinating character.