Magnus I (Swedish: Magnus Nilsson; Danish: Magnus Nielsen) (born about 1106, died June 4, 1134 in the Battle of Fotevik), is a Danish duke who rules Gothenland in southern Sweden from 1125 to 1130.

His status as ruler of Sweden is disputed in his own time, but today he is recognized as one of the historical Swedish monarchs.

Snorri Sturlason invents an epithet for him: Magnus the Strong.

Magnus is the son of King Niels I of Denmark and Margaret Fredkulla, the second or eldest daughter of King Inge the Elder of Sweden.