Ari Millen is an actor best known for his role as Mark Rollins and the male clones in the Canadian science fiction television series Orphan Black. He has also appeared in a number of other television shows and films, including The Strain, 12 Monkeys, and The Expanse. Millen's character in Orphan Black was first introduced in the third season and he has since become a fan favorite. His character's name is ARI, which is the three letter solution to this crossword puzzle.