The name Callahan is a boy's name of Irish origin meaning "bright-headed". Callahan and is often added to lists like Irish Boy Names - Baby Names and discussed in our forums with posts like "Make suggestions based on previous person's signature".
From the experts:
Callahan, the phonetic spelling of Callaghan, is a rhythmic jig of a name whose history harks back to the ancient King of Munster. In the Dirty Harry movies, the Clint Eastwood character is Harry Callahan.