Killian
Killian or Cillian, as a given name, is an Anglicized version of the Irish name Cillín. Killian is the more radical anglisation of the name as there is no 'K' in the Gaelic alphabet.
Killian, as a surname, is found in both Ireland and Germany. It was originally spelled Ó Cillín in Irish before being Anglicized into Killeen as well as Killian. Spelling variations for Killian include Kilian, Killion, and others.