Theoden was created by J. R. R. Tolkien for the king of Rohan in The Lord of the Rings, drawing on the Old English word theoden, which means "king" or "leader of the people". Parents use it as a fresh route to the nickname Theo. The name has climbed steadily in the United States, from number 5033 in 2015 to number 1632 in 2025, its best rank so far, with 104 boys.