Kolbeinn Tumason (Old Norse: [ˈkolˌbɛinː ˈtumɑˌson]; Modern Icelandic: [ˈkʰɔlˌpeitn̥ ˈtʰʏːmaˌsɔːn]; 1173–1208) was a member of the Ásbirningar family clan, and was one of the most powerful chieftains in Iceland around the turn of the 13th century. His power was probably at its height around 1200 AD. Kolbeinn used his influence to ensure that men in his favour received positions of power within the clergy, amongst them is bishop Guðmundur Arason. Guðmundur, unbeknownst to Kolbeinn, proved to be an advocate of clerical independence and resented interference from the secular chieftains. The two were soon at odds. In 1208, Kolbeinn and his followers attacked Guðmundur and his supporters in Hjaltadalur by Víðines. The ensuing battle is known as the Battle of Víðines. Kolbeinn died in the conflict, his head bashed in with a rock.