Thanos

Thanos is a villain who's main goal is to wipe out half of all life. So far, he has gotten the infinity stones twice, and failed once to snap.

Involvement in Story
Thanos first looked for the stones when the story first began, and the heroes had to fight for the stones, as they were being stolen by him. They successfully were able to stop him, and he was killed.

During his second attempt, Thor and Loki had just returned from Raganoark, and he already had the power stone. He proceeded to kill Loki so he could obtain the Space Stone, and fought Hulk, who he subdued. He killed Heimdall, who sent Hulk to Earth so he couldn't be killed.

When Thanos arrived on Earth, the Guardians of New York, and some of the Avengers began attacking him and the Black Order. He went to Vormir, and sacrificed Gamora, so he could get the Soul Stone.He was able to steal the reality stone, then threatened to kill everyone on Titan, if Strange didn't give him the Time Stone. He then went to Wakanda and killed Vision for the Mind Stone. When he was about to snap, he was impaled by Stormbreaker by Alfred, but he was still able to snap, eliminating 50% of all life in the universe.

He destroyed the stones, and was tracked down by the remaining heroes, and was beheaded by Thor. When the heroes eventually were all revived, The Earth 4 Thanos, who was still alive in his timeline, battled the heroes for the stones, and had all of them, but Shazam took the Gauntlet back, and snapped Thanos to limbo, thus ending his reign of terror.