Harald Klak
Harald 'Klak' Halfdansson (c. 785 – c. 852) was a king in Jutland (and possibly other parts of Denmark) around 812–814 and again from 819–827.
Read more about Harald Klak: Family, The Civil War of 812–814, Harald's Alliance With Louis The Pious, Return To Denmark and Later Life, Death, Heirs