Maximillion Pegasus, has had a number of different attempts few attempts on his life, in different series for different reasons.
Keith and Pegasus faced each other in a Duel in front of a large audience and on television. Pegasus made a fool of Keith by reading his mind and giving instructions to a child, Sam, to defeat Keith. Keith fell into a depressive slump and began to harbor a grudge against Pegasus.
Keith later infiltrated the Duelist Kingdom tournament to get revenge on Pegasus. He arranged a group of four Duelists including himself, Bonz, Sid and Zygor to try and cheat their way into the castle as the four finalists. However when that failed, he stole the other three's Star Chips allowing just himself to qualify as a finalist.
Keith failed to get a chance to Duel Pegasus after losing to Joey Wheeler in the semi-finals, so he attempted to kill him by pulling out a gun. (In the dub, the gun was removed). In the anime, Keith jumped up next to Pegasus with the gun, but Pegasus activated a secret switch, opening a trapdoor below Keith, causing him to plummet into the ocean. In the manga, Pegasus stopped him, by inflicting a Penalty Game, turning Keith's hand into a gun, which uncontrollably shot himself in the head.
In the anime, Yami Bakura engaged in a Shadow Game with Pegasus, who had been weakened after Dueling Yugi Muto and releasing the souls of Seto Kaiba, Mokuba Kaiba and Solomon Muto. Yami Bakura removed the eye afterwards, but it did not kill Pegasus.
Pegasus arrived at a Duel tournament in Domino City, in which Yugi Muto was a participant. When Paradox arrived, he sent "Stardust Dragon", "Rainbow Dragon", and "Cyber End Dragon" to attack the surrounding buildings. In the ensuing destruction, a building lost its stability and fell on Pegasus, killing him. The resulting disruption in the time stream was to cause people, buildings, schools, and cities that arose from the cultural impact of the card game to start to become erased. The Crimson Dragon appeared and took the only survivor, Yugi, back in time 30 minutes before Pegasus was killed. This time around, Yugi, Jaden Yuki, and Yusei Fudo's combined efforts stopped Paradox, thus the assassination was never completed. Pegasus landed via helicopter and gave out cards to children.