Jotuns, or Frost Giants, are a monstrous, ancient race of titans from the icy world of Jotunheim ruled by King Laufey. They have an ancient blood feud with the Asgardians, who've stolen their supremacy on the world.
Eons ago, the Frost Giants of Jotunheim attacked Earth armed with the Casket of Ancient Winters, but their invasion was thwarted by the Asgardians. Sent back to Jotunheim, Odin defeated the Frost Giant King Laufey before stealing the Casket and adopting the malformed Loki, Laufey's son. For centuries, Jotunheim was in a state of decay and hatred for Asgard.
In an attempt to prevent Thor's succession to the throne of Asgard, Loki aided a small band of Jotuns into Asgard to pillage Odin's Trophy Room, only for them to be killed by the Destroyer. Thor, Loki, Sif and the Warriors Three visited Jotunheim to ask recompense from Laufey, only to begin a bloody battle with them. The fight results in Laufey declaring war on Asgard, leading Odin to banish Thor to Earth as a mortal.
During Thor's exile, Loki learns that Laufey is his biological father and Odin falls into the Odinsleep, leaving Loki on the throne. Loki forms a pact with Laufey, offering him a chance to murder Odin in his sleep. Loki brings Laufey and a handful of giants to Asgard, only to kill Laufey moments before he can slay Odin, as part of a scheme to impress Odin. Thor reclaims his godly powers and seeks to defeat Loki, who unleashes the full power of Bifrost Bridge on Jotunheim, bringing devastating destruction to Jotunheim. Thor saves Jotunheim by destroying the bridge, cutting off Asgard's access to other worlds.
Frost giants are a very durable, long lived race, comparable to Asgardians. They appear to be physically stronger and taller than average Asgardians. They wear little if any armor in contrast to Asgardians, being very adapted to the cold, though they seem to be unaffected by Asgard's warmer climate.
Frost Giants have the ability to form ice out of moisture from the atmosphere or perhaps even from their own bodies and shape it into tools like blades, spiked throwing balls, or solid ice pillars that can knock an Asgardian down. The ice made by Frost Giants is obviously far harder than normal ice as it can injure Asgardians while bullets bounce off of Asgardians. The ice is however not as tough as Uru, for one of Loki's thrown knives shattered a Frost Giants ice blade.