One of the Marvel Universe's greatest scientists, the Beast has been a member of the X-Men since its original lineup. Not only that, the Beast has also been a member of the Avengers and the Defenders, a feat rarely seen before the 2000s. Overall the Beast is very well established to be a heroic character, with him, Angel and Iceman being the members of the original five who have become villains at any point.
Despite being a superhero for his nearly sixty years of existence, the Beast has committed a lot of morally dubious actions. Here are some of his worst.
10 Involved In The Creation Of MGH
While comparing to the other things on this list, this action was not directly the Beast's fault. The Beast, however, played a central role in allowing the creation of the drug Mutant Growth Hormone. The Beast's research on the hormones that caused mutations to occur in Mutants was turned by his employer, the Brand Corporation, into the dangerous drug MGH.
MGH would later be used to empower various Supervillian to cause more destruction than they would with their regular power. Most infamously an MGH boosted Nitro would blow up the town of Stamford, Connecticut leading to the events of Civil War. The drug's addictive nature also destroyed the lives of many superhumans and wannabe ones.
9 Pretended To Be Gay
Grant Morrison's New X-men run was not particularly kind to the Beast. He was beaten unconscious by a mind-controlled Beak in the first story arc. A more self-inflicted problem the Beast face during Morrison's run was that Beast pretended that he was gay. This lie soon begets other ones.
Beast started to pretend to be gay when he claimed that he might be gay to stop his ex-girlfriend Trish Tilby from renewing their relationship. Because he made that statement in a public situation, some people report that Beast was gay. Instead of disproving those rumors, the Beast decides to declare that he was gay in a misguided attempt to promote tolerance.
8 Siding With The Inhumans
During the leadup to the Inhumans vs. X-Men, Beast ended up working with the Inhumans. While this was initially done by the Beast to secretly help the X-Men develop a cure for M-Pox., the Beast strayed in his loyalty. This straying was a result of the X-men kicking him off the team, eight months earlier, for his tampering in the time stream.
This would lead to the Beast betraying the X-Men during Inhumans vs. X-Men. He would betray the X-men by attempting to warn the Inhumans of the X-Men's plan to attack them. Beast was, however, captured by the X-Men before he could warn the Inhumans.
7 Working With The Dark Beast
The Beast following the events of M-Day would devout all of his efforts to figure out a way to reverse it. This would lead to the Beast seeking out the aid of the Marvel Universe's greatest scientists, both good and evil. This effort would lead to the Beast forming a partnership with his evil counterpart from the Age of Apocalypse, the Dark Beast.
This partnership would see Beast aiding Dark Beast in recovering his equipment from S.H.I.E.L.D and examining corpses on Genosha. This partnership ended when the Beast discovered that Dark Beast was injecting non-Mutant children with a serum in a brutal attempt to turn them into Mutants.
6 Gave Threnody Over To Mister Sinister
Beast's action post-M-day was not the first time that the Beast would work with a villain in the name of saving Mutantkind. During the emergence of the Legacy Virus in the 1990s, the Beast made a deal with Mister Sinister. That deal being that Beast would leave the young mutant Therondy with Mister Sinister, in the hope that he could develop a cure for the Legacy Virus using her mutant power.
Of the worst thing that the Beast has done, this is one of the few things he was sorry about. This can be seen by the Beast trying tp free Threnody the next time he encounters her.
5 Attempted To Force Hadwin Cocom Into A Coma
The recent X-Force series seems to be moving the Beast into a darker direction as the head of Krakoan intelligence. This is most apparent in the series' sixth issue when the Beast forced Hadwin Cocom, son of the president of Terra Verde, into a coma. The Beast did this to both punish him for his anti-mutant activity and that he hopes to use the president's grief to make it easier for Terra Verde to consider an alliance with Krakoa.
This plan did not correctly as Hadwin was already mutated into a plant-like creature and soon awaken as a plant-like monster. Hadwin would then help the awakening of Muerte Verde leading to the whole of Terra Verde to be taken over by a race humanoid plant creature.
4 Caused The 1906 San Fransico Earthquake
While indirectly caused by the Beast, he still causes one of the worst natural disasters in American history. During a time travel trip to San Fransico in 1906 to find Dr. Nemesis' parent and the origins of Mutantkind, the X-men encountered the Hellfire Club. The Hellfire Club worried about the coming rise of Mutantkind created a giant robot to hunt them down before they could become a threat to their influence.
The Beast and his fellow X-men would enter a heated battle with this predecessor to the Sentinels. The battle would lead to the robot's power source exploding. The energy of this explosion would be the cause of the 1906 San Fransico Earthquake.
3 Bringing The Five Orignal X-men To The Future
A notable case of good intentions that go wrong, the Beast decided to bring the original five X-men into the future. He was hoping to use a younger version of the original X-men to convince Cyclops to stop his current plans of war against all of Humankind. This plan did not work out and the young X-men decided to stay in the present.
This would have a decision would have major consequences in that there are now five potential time paradoxes walking around the Marvel Universe. This would lead to the Extermination storyline, where several parties forced the young X-men to return to the past before they could cause the apocalypse.
2 Modified The Legacy Virus To Infect The Skrull
The X-men tie-in with the Secret Invasion saw the Beast go in a dark direction to stop the Skrull invasion of San Fransico. The Beast decides to mutated the Legacy virus to infect only Skrulls, as a potential last resort for the X-men. Cyclops would then unleash the modified virus on the Skull fleet invading San Fransico.
The modified virus was successful in taking out the fleet, as the fleet's commander decided to destroy his fleet to prevent the virus from spreading to the rest of the Skrull race. Cyclops unleashing the virus would help to strain the relationship between himself and the Beast leading, leading to Beast siding with Wolverine during Schism.
1 Aided The Illuminati In Destroying Several Alternate Earths
During Johnathan Hickman's run on New Avengers, The Beast was invited to replace the recently deceased Professor X's on the Illuminati. Shortly into his tenure, Beast would aid the Illuminati in their effort to preserve Earth from the destruction of the Multiverse. This effort would see Beast commit the worst thing he has ever done.
That thing being that he aided the Illuminati in destroying a bunch of alternate Earths to prevent them from colliding with their Earth. They would also take out any inhabitant of those alternate Earths that tried to stop them. This effort would be for naught as the Earth was destroyed colliding with the Ultimate universe version of Earth.