Frotho I is one of the legendary Danish kings

Legendary Danish kings

The legendary kings of Denmark are the predecessors of Gorm the Old, half history and half legend. The accounts of the Danish kings are confusing and contradictory, and so this presentation tries to separate the various sources from each other...

 in Saxo Grammaticus

Saxo Grammaticus

Saxo Grammaticus also known as Saxo cognomine Longus was a Danish historian, thought to have been a secular clerk or secretary to Absalon, Archbishop of Lund, foremost advisor to Valdemar I of Denmark. He is the author of the first full history of Denmark.- Life :The Jutland Chronicle gives...

' Gesta Danorum

Gesta Danorum

Gesta Danorum is a patriotic work of Danish history, by the 12th century author Saxo Grammaticus . It is the most ambitious literary undertaking of medieval Denmark and is an essential source for the nation's early history...

where he has a substantial biography. He succeeds his father Hadingus

Hadingus

Hadingus was one of the earliest legendary Danish kings according to Saxo Grammaticus' Gesta Danorum where he has a detailed biography. Georges Dumézil and others have argued that Gram was partially modelled on the god Njörðr.-Gesta Danorum:...

 to the throne and replenishes the war-drained treasury by slaying a dragon

Norse dragon

In Norse mythology there are several references to dragons.* In the Völuspá the being Níðhöggr is identified as a dragon * The Midgard Serpent is described as a giant, venomous serpent...

 and winning its treasure. He uses the money to finance expeditions into the Baltic

Baltic Sea

The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

 where he wins victories with clever strategems (including one where he crossdresses as one of his own shieldmaiden

Shieldmaiden

A shieldmaiden was a woman who had chosen to fight as a warrior in Scandinavian folklore and mythology. They are often mentioned in sagas such as Hervarar saga and in Gesta Danorum. Shieldmaidens also appear in stories of other Germanic nations: Goths, Cimbri, and Marcomanni. The mythical Valkyries...

s). After some trouble at home he campaigns successfully in Britain

Britannia

Britannia is an ancient term for Great Britain, and also a female personification of the island. The name is Latin, and derives from the Greek form Prettanike or Brettaniai, which originally designated a collection of islands with individual names, including Albion or Great Britain. However, by the...

 and captures London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

. He finally dies in a war against the king of Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

.
See also: Fróði

Fróði

Fróði is the name of a number of legendary Danish kings in various texts including Beowulf, Snorri Sturluson's Prose Edda and his Ynglinga saga, Saxo Grammaticus' Gesta Danorum, and the Grottasöngr. A Danish king by this name also appears as a minor character in the Middle High German epic Die...