Citadel Billionaire Ken Griffin Defends Melvin Stake Against ‘an Insane Conspiracy Theory’ (CNBC) Ken Griffin, the billionaire CEO of hedge fund Citadel, defended his $2 billion investment in short seller Gabe Plotkin’s Melvin Capital last month amid the height of the GameStop mania. “No, I think Gabe Plotkin is one of the finest investors of his generation,” Griffin told CNBC’s Andrew Ross Sorkin on “Squawk Box.” The comment was in response to a question from Sorkin about whether Griffin’s investment was a mistake because it created questions about Griffin’s motivations in propping up Plotkin amid his battle with retail Reddit traders who were pumping up the price of GameStop.