Magnús góði Guðmundarson (or Guðmundsson; 1172 – 20 September 1240) was a medieval chieftain (gothi) of Þingvellir in Iceland.
He inherited the office from his father Guðmundr gríss Ámundason, who was the descendant of Ingólfur Arnarson, one of the first Viking settlers on the island.
He had no offspring, and contemporary sources only offer conjectures about his successor, possibly Árni óreiða Magnússon, nephew of Guðmundr gríss Ámundason and son-in-law of the skald Snorri Sturluson.
[1] In fact, the sagas narrate that Sturluson caused Magnús's fall: during his first term as lawspeaker, Sturluson convinced the Althing to outlaw (skógarmaðr) Magnús.
[2] According to konungsannáll, Magnús obtained the support of the clans Haukdælir, Oddaverjar and Svínfellingar to become bishop of Skálholt in 1236, but he did not obtain the Apostolic Blessing since he did not fulfil the requirements for the position; his candidacy was approved neither by the Norwegian archdiocese nor the Pope.