The Blue Devil was one of many nominees in a 1921 contest to determine a university nickname. Blue Eagles, Royal Blazes, Blue Warriors, and Polar Bears were also considered. The contest ended with no conclusive winners, but the student newspaper started to refer to the university’s teams as the Blue Devils anyway, and it eventually caught on.

The name was inspired by the Chasseurs Alpins, a group of blue cape- and beret-wearing French soldiers, who were nicknamed "les Diables Bleus." They were known for their courage during World War I, and even raised money in support of the war effort in the United States.

Many more mascot origins here.