Spider-Man

Spider-Man was a well known hero, before he was eventually lured and killed by the Sinister Six.

Involvement in Story
Spider-Man was one of the people who helped first fight off Thanos, and died after being injured severely by him, at first.

Spider-Man soon became evil and hungry for power, and destroyed buildings in New York to satisfy his greed. He went on a crime spree with Darkseid, and died multiple times, getting taught how to come back to life by Tony multiple times. He was eventually stopped, and reverted back to his normal state.

After that, he was lured in by the Sinister Six, who wanted to kill him, and they all teamed up, and used their attacks to easily subdue him, then finished off him off to kill him.

He eventually came back after being revived, and continued being a superhero normally until he clashed with the new Sinister Six once again, who attacked his family and ruined his personal life, which led him to his eventual suicide later.

Legacy
He was succeeded by Miles Morales, who became the 2nd Spider-Man after his death. While he was not mourned by most people, Tony Stark was greatly affected emotionally.

While he eventually returned, he still died later after committing suicide from the stress and horrors he experienced during his second run as Spiderman.