Kalv Arnesson

Kálfr Árnason (; – 1051) was an 11th-century Norwegian chieftain who played a major role both in defeating King Olaf Haraldsson (later named St. Olaf) at the Battle of Stiklestad and in bringing back his young son Magnus and raising him to the throne.

Life Kálfr was a son of Árni Arnmódsson or Armódsson and Þora Þorsteinsdóttir. Finn Árnasson (died ) and Þorbergr Árnasson (died c. 1050) were his brothers.

In the 1020s and 1030s, he was one of the most powerful chieftains in Norway. He was married to Sigrid Þorisdóttir, sister of Thorir Hund, and his sister Ragnhild was married to Hárek of Tjøtta. According to the one contemporary source which mentions Kálfr, the Kálfsflokkr, by the Icelandic skáld Bjarni gullbrárskáld, he was at Olaf's side in the battle against Erling Skjalgsson. After the latter's death, Olaf was forced to flee Norway in 1028, and Kálfr supposedly went to England and pledged his support to Cnut the Great of Denmark, who became king of Norway that year.

When Olaf returned in 1030 to attempt to regain his kingdom, according to the skaldic poem, Kálfr was one of his strongest opponents. According to the sagas, however, his brothers remained loyal to Olaf. Scholar Claus Krag sees echoes of Judas kissing Jesus in the scenes in Heimskringla between Kálfr and Olaf. however, the poet merely describes him as "[fighting] ... stout of heart ... until that fallen lay the liege-lord", and according to another skáld, Sigvatr Þórðarson, Thorir Hund struck the fatal blow.

Kálfr was initially the most influential advisor of the young king, but later fell into disrepute with him, probably because of Einar's ambition to be his most powerful advisor; He spent a number of years abroad, in Ireland and the Hebrides. In 1050, Magnus' successor, Harald Hardrada, asked him to return, but only to send him to fight in Denmark, leading to his death in about 1051. His brother Finn regarded the king as having treated Kálfr deceitfully and broke with him over it.