In all honesty, Ron-Karr really never wanted to be a villain.
The Neptune native originally applied for the Legion of Super-Heroes, showcasing his ability to turn himself two-dimensional. He was rejected, and the dejected teenager fell in with Tarik the Mute and his Legion of Super-Villains, more out of a desire to belong than any feelings of malice or superiority.
His contribution to any of the battles he participated in was negligible; he wasn't bloodthirsty or combative by nature. He skirted interacting with the more sociopathic members of his team, and when he did speak up, he was more than anything a timid voice of reason. Eventually he disconnected from the group.
His streak of bad memberships continued into the Five Year Gap storyline, where he joined up with one of Universo's pockets of resistance. The leader of the group, Grinn, was less than enthused to have the former LSV member amongst his ranks. When the crew eventually met up with Jacques Foccart and the Substitute Heroes, Ron-Karr finally found a group that welcomed him warmly and weren't a bunch of murderers.
Ron-Karr honed his flattening and stretching abilities, filled with newfound pride in belonging for once, and contributed with pride during the war with the Dominion. Afterwards, he stuck with his Subs teammates and became an instructor at the United Planets Militia Academy.
Ron-Karr makes an appearance as a statue.
In other media
In the Legion of Superheroes animated series Ron-Karr appears as a shapeshifter.