While Marvel's Thor is the God of Thunder and one of the universe's mightiest beings, his father Odin is known to wield one of the most powerful forces of magic in existence. The Odin Force, also known as the Power of the All-Father, has been historically wielded by Odin. However, Thor recently claimed it for himself when he took over as the All-Father in the wake of War of the Realms, and he now calls it the Thor Force.
Along with his recent Power Cosmic upgrades, this force is the God of Thunder's ultimate power boost. Even though they're gods, Asgardians such as Odin and Thor occasionally require a boost in power to face foes on a cosmic scale. Both of them have summoned the Odin Force on multiple occasions, in both the comic book Marvel Universe and the Marvel Cinematic Universe, to boost their powers to near-infinite strength.
Long ago, Odin found himself battling Surtur, the God of Muspelheim and King of the Fire Giants who was destined to destroy the Nine Realms. with his two brothers Vili and Ve. Though the Asgardians were victorious in destroying the sword Surtur claimed he would use to destroy their worlds, Surtur would emerge and blast three brothers. Odin would later awaken realizing his two brothers were dead, but that he now held their combined powers, thus creating the Odin Force, as recalled in Walter Simonson's Thor #349.
While the limits of the Odin Force are currently unknown, the sheer magnitude of its power requires its user to occasionally enter a deep sleep, known as the Odin-Sleep, to replenish their power. It also seems to have a form of sentience, once taking the form of a fallen Asgardian child to converse with Thor.
The Odinforce has done everything from assisting Thor in destroying Captain America's virtually indestructible shield to helping Odin create a galaxy that he then used it to destroy to allowing Thor to remove two nuclear warheads from his chest, It was even used by Odin to cut our the heart of a star that he then used to forge and empower Mjolnir, and to restore Thor, Valkyrie and all the lives in Asgard that were lost during Ragnorak.
In the Marvel Cinematic Universe, the Odin Force has also made several appearances, either via Odin's staff Gungnir or other means. In Thor, Odin uses it to disintegrate a squad of Frost Giants that have invaded his vault. After banishing Thor from Asgard, Odin then falls into the Odin-Sleep which grants Loki the Odin Force that he later uses to battle his brother. Blasts of the Odin Force were weaponized by S.H.I.E.L.D., which Phil Coulson later used on Loki in The Avengers. Its later appearances see Odin using it to convert a fallen Frigga into energy in Thor: The Dark World before dissolving into it himself in Thor: Ragnarok.
So far the MCU hasn't been shy in its use of the Odin Force, but we have yet to see it in full effect or used by Thor at all. Although the comic version of Thor has recently been seen sporting the power cosmic in his adventures as a herald of Galactus, the Odin Force still stands as his ultimate upgrade.