Thanks to arrowshieldfan for the heads up.
Here's the official description of the character: "Lonnie Machin (AKA Anarky) is a deranged freelancing criminal who is willing to do whatever it takes to impress a potential employer."
The Ben and Kate alum will play Curtis Holt, aka Mr. Terrific. Holt is a technological savant and inventor who works at Palmer Technologies under the supervision of Felicity Smoak (Emily Bett Rickards).
In the comics, Mr. Terrific’s alter-ego is Michael Holt, an extremely intelligent Olympic-level athlete who joined the justice Society of America following the death of his wife and unborn child.
Kellum will first appear in episode 2.