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 on Friday told CNBC’s Andrew Ross Sorkin during 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 the shares of GameStop.

“If I had to run my business on the possibility of an insane conspiracy theory emerging at any point in time, I would have no business,” Griffin said.

Besides running hedge fund Citadel, Griffin is the founder of dominant market-maker Citadel Securities, which handles about 40% of U.S. retail stock order flow, including from brokerages like free-trading app Robinhood.

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