Ron-Karr was one of the founding members of the Legion of Super Villains.
Ron-Karr was a native of Neptune. As such, he had the power all of his race have: the ability to flatten his / her body. He applied for the Legion of Super Heroes (the premiere superheroes of the 30th and 31st century), but was rejected. He joined the Legion of Super-Villains and wasn't helpful in their attempts to kill the LSH. He gave up being evil and joined the Legion of Substitute Heroes (a team of Legion of Super Heroes rejects).
Ron-Karr originally appeared in Adventure Comics #314. In this comic, his name is spelled "Ronn Kar". However, everywhere else his name is spelled "Ron-Karr" (hence the title of this post).