He later came back to Star City to help Team Arrow track down Emiko Queen and her biological weapon.
Echo Kellum first appeared as Curtis Holt on Arrow in Season 4 as a recurring role before being upped to series regular in the fifth, sixth and seventh seasons.
Kellum left the series towards the end of Season 7, but appeared in three episodes of the show’s eighth and final season, including the series finale.
After his time with Team Arrow as Mr. Terrific was done, Curtis had accepted a new job in Washington, D.C. after he left A.R.G.U.S. following a disagreement over the decision to revive the Suicide Squad under the Ghost Initiative.