Unlike the rest of the group on this list, Aidan Gallagher technically plays the younger and mentally-older version of himself. His older physical self is played by Sean Sullivan, who we get to see more of during season two. Gallagher is probably best-known for his role as Nicky on Nickelodeon's Nicky, Ricky, Dicky & Dawn. Based on his performance on The Umbrella Academy it's hard to believe he's not had anything but a few one-off appearances on random shows prior to landing the Netflix show.