Frotho I is one of the legendary Danish kings in Saxo Grammaticus' Gesta Danorum, where he has a substantial biography.
He succeeds his father Hadingus to the throne and replenishes the war-drained treasury by slaying a dragon and winning its treasure.
He uses the money to finance expeditions into the Baltic, where he wins victories with clever strategems (including one where he crossdresses as one of his own shieldmaidens).
Superscript numbers before a name indicate in which books of Gesta Danorum the individual is mentioned.
Name spellings are derived from Oliver Elton's 1905 translation, The First Nine Books of the Danish History of Saxo Grammaticus, via Wikisource.