Callen is a modern spelling of Callan, an Irish surname usually explained as "battle" or "little warrior", from the Gaelic cath; some parents also hear it as a smoother relative of Cullen. The character G. Callen on NCIS: Los Angeles, played by Chris O'Donnell from 2009, put the spelling on the map. Callen entered the US top 1000 in 2010, peaked at number 450 in 2023 and ranks number 516 in 2025.