In Norse mythology Beli is probably a giant. He was killed by Freyr.
In scaldic and Eddic poetry, Freyr is sometimes called "Beli's enemy" (Belja dólgr, in Eyvindr skáldaspillir's Háleygjatal, 3) or "Beli's slayer" (bani Belja in Völuspá, 53). How Freyr killed Beli is told by Snorri Sturluson in Gylfaginning (37) during the recounting of the wooing of Gerðr. The circumstances surrounding the event are not given but it is stated that since Freyr had given his sword to his servant Skírnir before sending him to court Gerðr, he was weaponless and therefore used the antler of a hart to kill the giant. When Gylfi expressed wonder that Freyr would give up his sword, Hárr dismissed his concern by saying that Freyr could have killed Beli with just his bare hands if he so wished, but then added that he would indeed regret his decision during the upcoming time of Ragnarök when Freyr would have to fight the sons of Muspell.
In Þjóðólfr of Hvinir's, Haustlöng (18). Þjóðólfr uses the kenning "Beli's bale-troop" (bölverðung Belja) to refer to the giants of Jotunheim, suggesting Beli to be a leading warlord among the Ettings.
It is sometimes assumed that Beli was Gerðr's brother, based on stanza 16 of Skírnismál where Gerðr expresses her fear that the unknown man who has come to visit is her "brother's slayer".