He attempted to kill the Cooper Clan for generations.
While his attempted murders are mainly off-screen, there is on-screen evidence that proves this. In his introduction scene in the first game, he is seen in the background of pictures with 4 of Sly's ancestors in the Thievius Raccoonus, which establishes a pattern of trying to kill the Coopers.
He hypnotized Henriette "One-Eyed" Cooper's shipmates in an attempt to kill her, endangering dozens to hundreds on her boat with her only barely escaping Clockwerk before he could kill her due to her eye patch granting her immunity to his hypnosis.
He killed Sly Cooper's father, Conner (and possibly his wife too), and stole the Thievius Raccoonus's pages with the rest of the Fiendish Five. He only spared Sly as a child to try and show the world that his family was useless without the knowledge from the book, leaving a young Sly as an orphan.
As the founder and leader of the Fiendish Five, he is responsible for all the crimes his fellow members would commit, including Sir Raleigh sinking at least 50 ships and the Panda King using fireworks to cause avalanches that bury entire villages in snow.
He attempted to kill the Cooper Gang with his Robo-Falcons, Lava Slugs and death ray.
He kidnaps Carmelita Fox and uses her as bait to lure Sly into his gas chamber, which would have killed the two if not for Bentley hacking into the system. He then mocked Sly after falling into his trap, laughing at him and claiming that "empathy has always been the downfall of the Cooper Clan."
He is indirectly responsible for the events of the second game, as the Klaww Gang would use his body parts for their own criminal activities, with their leader Arpeggio planning to reconstruct his body and hypnotize all of Paris with spiced food into a hateful frenzy in order to become immortal.
The game also makes it repeatedly clear that had he succeeded in reactivating Clockwerk, he would have continued to antagonize Sly and his future descendants until he finally killed off the Coopers for good.
After Constable Neyla took control of his body, some of his influence spread to her, causing her to become even more evil than she originally was. This also made him responsible for Clock-La crippling Bentley for the rest of the series, which caused Murray to blame himself and temporarily leave the Cooper Gang.
His observation on the Cooper Clan and the Cooper Gang, as well as one of his eyes that could be obtained as a collectible treasure during Thieves in Time, has implied that he had survived the destruction of the Hate Chip, possibly planning to make a return. Another hint is that Clockwerk can be seen watching the Cooper gang in 10,000 B.C. This would contradict his statement in being alive for centuries unless he somehow managed to go in that time period.
Overall, Clockwerk is so irredeemably evil that he is one of the very few criminals Carmelita is willing to kill instead of putting away in jail.
Unlike many Sly villains who had some sort of redeeming qualities and/or tragic backstory (with a few exceptions like General Tsao, Constable Neyla and Sir Raleigh), Clockwerk has none as his only motivation is nothing more than pure, envious spite for the Cooper family.


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