"Hagbard's gallows", a megalithic monument in Asige, Halland, Sweden.

Hagbard (Old Norse Hagbarðr), the brother of Haki and son of Hamund, was a famous Scandinavian sea-king in Norse mythology. He is mentioned in Skáldskaparmál, Ynglinga saga, Nafnaþulur, Völsunga saga and Gesta Danorum. The heroes' connections with other legendary characters place the events in the 5th century AD.

Hagbard remained well-known until recent times in the legend of Hagbard and Signy. This famous legend tells that Hagbard fell in love with Signy, the daughter of king Sigar, the nephew of king Siggeir (of the Völsunga saga), a love affair which ended in their deaths, when Sigar wanted to have Hagbard hanged. This legend is told most fully in Gesta Danorum (book 7).

However, most legends surrounding Hagbard are probably lost. In the Völsunga saga, Gudrun and Brynhild have a discussion on the "greatest of men" referring to a legend now lost, where Hagbard is mentioned together with Haki's sons, who have not yet avenged their sisters by killing the evil Sigar (the feud with Sigar is still going on and Hagbard not yet hanged):

Snorri Sturluson wrote in the Ynglinga saga that Hagbard occasionally plundered together with his brother Haki. Concerning, the adventures and death of the Swedish king Jorund (whom Snorri makes a successor of Haki), he cites the poem Háleygjatal by a Norwegian skald named Eyvindr skáldaspillir containing the Kenning Sigar's steed referring to the legend of Hagbard and Signy:

En Guðlaugr
grimman tamdi
við ofrkapp
Sigars jó,
er synir Yngva
við meið reiddu.
Og náreiðr
á nesi drúpir
þar er víkur deilir,
þar er fjölkunnt
um fylkis hreyr
steini merkt,
By the fierce East-kings' cruel pride,
Gudlog must on the wild horse ride --
The wildest horse you e'er did see:
'Tis Sigur's steed -- the gallows tree.
At Stromones the tree did grow,
Where Gudlog's corpse waves on the bough.
A high stone stands on Stromo's heath,
To tell the gallant hero's death.[4][5]

The same kenning appears with Hagbard's name in a stanza from Ynglingatal, which Snorri also quotes in the same section:

Varð Jörundr
hinn er endr of dó,
lífs of lattr
í Limafirði,
þá er hábrjóstr
hörva Sleipnir
bana Goðlaugs
of bera skyldi;
ok Hagbarðs
hersa valdi
höðnu leif
at halsi gekk.[3][6]
Jorund has travelled far and wide,
But the same horse he must bestride
On which he made brave Gudlog ride.
He too must for a necklace wear
Hagbert's fell noose in middle air.
The army leader thus must ride
On Horva's horse, at Lymfjord's side.[4][5]