Loki Laufeyson

From the first Thor movie to the end of Avengers, Loki's personality is a whirlwind of emotional neediness disguised as megalomania. He transitions from a neglected and calculating son, who discovers he is the monster from bedtime stories (the "Ice Giant"), to a wounded tyrant who seeks in the dominion of Earth the recognition he never felt he had in Asgard.
His essence is defined by ambivalence: he is the master of trickery and sarcasm, using intellect and manipulation as shields for a deep vulnerability. Loki doesn't just want power for power's sake; he wants a throne to prove he is equal to Thor and superior to the fate of "second son." He is theatrical, arrogant, and volatile, but his villainy in New York is, at its core, a desperate cry from an outsider who prefers to be hated and feared rather than ignored.

The Shadow of the Second Son
Loki grew up in Asgard believing himself to be a prince by blood, but always lived in the shadow of Thor's brute strength and charisma. While his brother was celebrated, Loki was merely tolerated. He developed mastery of magic and persuasion not by choice, but out of necessity, to survive in a world that valued warriors.
2. The Monster's Revelation
The big turning point occurs in Thor (2011), when Loki discovers the truth about his origin: he is not Odin's son, but rather Laufey's, the king of the Frost Giants—Asgard's greatest enemies. He was "rescued" (or kidnapped) by Odin as a baby to serve as a political tool in the future. This revelation shatters his identity. He feels that his father and brother have deceived him his entire life and that he is, in fact, the monster from the bedtime stories he has learned to hate.
3. Sacrifice and Emptiness
In a desperate attempt to prove his loyalty to Asgard and his worth to Odin, Loki tries to destroy Jotunheim (his home planet). After being confronted by Thor and met with a disapproving look from Odin, he chooses to release the Bifrost bridge and plunge into the abyss of the cosmos, preferring possible oblivion to the failure of being "just a monster".
4. The Pact with the Titan
In the void of space, Loki is found by Thanos and the Other. Tortured and influenced by the Mind Stone in the Scepter, his resentment transforms into a purified hatred. He makes a deal: command of a Chitauri army to conquer Earth in exchange for the Tesseract.
5. The Invader of New York
In The Avengers (2012), Loki arrives on Earth with the demeanor of a tyrannical king. He uses the rhetoric that humans were "made to be ruled" and that freedom is a lie. He wreaks havoc in Germany, kills Agent Coulson, and opens the portal over New York. However, his arrogance blinds him: he is defeated by the Hulk's brute strength and the unlikely alliance of the Avengers.