Regan comes from the Irish surname Ó Riagáin and is usually explained as "little king", from rí, king, with a diminutive ending, or as "impulsive". Shakespeare used it for one of King Lear's daughters, and it is the original spelling behind the more common Reagan. For girls Regan peaked at number 391 in 2001 and has slipped out of the US top 1000, ranking number 2295 in 2025.