ALTERNATE VERSIONS
Pietro has always been over-protective of his sister, but in the alternate reality presented in What If? (2nd series) #5 his obsessive need to protect her had tragic consequences. In this timeline, Wonder Man joined the Avengers much earlier, and the Scarlet Witch found herself immediately attracted to him. Simon Williams returned her romantic interest, but Pietro objected to Wonder Man’s advances and made Wanda promise not to pursue her growing feelings for Wonder Man. For a time, she honored her agreement with Pietro until she and Simon found they could no 
longer deny their feelings and declared their love for each other. Enraged, Pietro abandoned the team and rejoined Magneto’s Brotherhood. Making use of Pietro’s hatred of Wonder Man and the Avengers, Magneto manipulated Quicksilver into donning the identity of the Grim Reaper and attacking his former teammates. After his defeat, Pietro was unmasked to the shock of his sister. In a subsequent battle between the Avengers and Magneto’s forces, the master of magnetism tried to kill Wanda for betraying mutantkind. Unwilling to see Wanda hurt despite his earlier statements, Quicksilver pushed her out of the way and was crushed beneath the heavy machinery Magneto tried to topple on Wanda. He was killed instantly. Overcome by grief, Wanda turned her hex power on Magneto causing his body to explode from within.
In the Age of Apocalypse, the early death of Charles Xavier inspired his friend Magnus to form the X-Men in far off Wundagore. Magneto’s original team of mutants, dedicated to Xavier’s dream of peaceful human/mutant coexistence, included his children Pietro and Wanda as well as Colossus, Jean Grey, Storm and Iceman. Whereas the Scarlet Witch was killed by an enemy very early on, Quicksilver remained a mainstay of the team during it’s many incarnation and eventually was given his own squad to lead, the other half of the team being under the command of Magneto’s wife, Rogue.
Pietro was rather obliged to his duties, though he rarely allowed himself to show his emotional side. Fighting side-by-side with her for years, he eventually developed romantic feelings for Storm.
After years of conflict with Apocalypse, Quicksilver and the X-Men turned the corner with the death of the Eternal One and forged a human - mutant government alliance as official state heroes, with his father as head of the Bureau of Mutant Affairs. However, sinister forces continued to exist in America, and Quicksilver eventually died in battle with Essex and his Sinister Six.
Quicksilver’s life came to an end at the second wedding of Hank Pym and Janet Van Dyne in the potential future depicted in the Last Avengers Story. Long-brewing tensions between Pietro and his sister’s husband, the Vision, finally came to a head that day, resulting in a full-blown battle between the two. When Wanda tried to stop the fight she got caught in the middle… literally. She was crushed between her speedster brother and the diamond-hard body of her synthezoid husband. Wanda’s death led to Pietro’s immediate suicide and the Vision went mad and allowed the molecules of his body to drift apart.
In the divergent timeline depicted in What if (2nd series) #96, Magneto was able to save his first daughter, Anya, and his wife did not run away. As such, Magnus was present when she gave birth to the twins. Well aware that mutants were feared, the small family lived a rather secluded life, and Magneto forbade his children to venture into the world of the humans. 
However, Pietro was curious and, after his mutant powers manifested, he ventured into a nearby city. He built himself a new life away from his family, meeting girls and eventually becoming a successful and famous athlete. For a while, he stayed in contact with Wanda, but when she no longer answered his letters, Pietro returned home only to learn that his sister had disappeared. His legs being crushed in a motorcycle accident ended his career, and Pietro was confined to a wheelchair. Having nothing else to do, he started snooping around and found evidence that Wanda had been killed... by their father. After Pietro avenged her death and shot Magnus, Anya revealed that she was the one who had killed Wanda and framed their father for it. Her entire life she had felt left out, with Magnus always favoring his two mutant children. In the long run, though, she had proven superior to all of them.
When Morgan le Fay used the Twilight Sword to reconstruct reality to her whims, the entire world was blasted back to medieval times. She kept the Avengers, who had opposed her, around as her personal royal guard, the Queen's Vengeance. Quicksilver was recreated as Gypsy Davy.
Fortunately, some Avengers remembered that this was not how the world was supposed to be and eventually the Scarlet Witch could use her teammates‘ united energies to disrupt Morgan’s spell and reality was restored.
The House of M reality was created when Quicksilver whispered in his sister's ear, causing her to rewrite reality into a new world where she could be safe and mutantkind was ascendant. Pietro and Wanda Magnus of the House of Magnus served under their father Magneto, undisputed ruler of America and claimant to the entire world. Pietro acted as a royal prince under Magneto as he tried to consolidate his power on the outlying regions of the globe. Magneto wanted Pietro to woo the mutant queen Ororo in Africa before the human king of Wakanda, T'Challa, swept her up as an ally against the House of Magnus.
On Battleworld, another version of the House of M existed. In this slice of reality, Pietro was an intended usurper, joining forces with Namor to remove his father from the throne and declare himself king. His sister Lorna remained loyal to Magneto, however, who also gained unexpected allies in the Human Resistance. Although Magneto was temporarily depowered, he restored his magnetic abilities and disposed of Namor easily. Blood was thicker than water, and Magneto forgave Pietro for his betrayal, although Lorna was not so quick to forget.
Pietro’s counterpart seen in the Mutant X universe wore a costume that covered his entire boy from head to toe, including a helmet in a streamlined, aerodynamic shape. He joined the X-Men after his father, Magneto, denounced his criminal ways and became the group’s leader. While his sister Wanda remained with the Avengers, Quicksilver’s half-sister Polaris was also among the X-Men. For reasons unknown, though, Lorna and Magneto had a much stronger bond than Pietro with either one of them. When most of this reality’s heroes gathered together to fight the combined threats of the Beyonder, Dracula and the Goblin Force, Quicksilver was just one of numerous casualties.
The Quicksilver of the Ultimate universe is not too far removed from his counterpart in the main reality. However, one difference is that Pietro was fully aware of his relationship to Magneto and 
willingly served him in his Brotherhood of Mutant Supremacy. At least, for a time. The entire dynamics of Magneto’s family seemed extremely dysfunctional, given the incestuous relationship of Wanda and Pietro and the tough love Magneto gave Quicksilver which bordered on psychological manipulation. When Magneto controlled dozens of Sentinels and sent them to Washington to destroy humanity, Quicksilver aided the X-Men by removing his father's helmet (at super speed so Magneto could not stop him).
The siblings assumed leadership of the Brotherhood during a time that Magneto was believed dead, and they even attacked a military convoy in an effort to recover their father’s body. After the Brotherhood disbanded, it was Quicksilver who decided he and Wanda should go to work as covert operatives for the US government’s team - the Ultimates. Quicksilver quickly proved his worth as a member of the Ultimates while battling an insane Thor. However, the true test was when the Ultimates were called in to battle Magneto, who had not perished as the twins initially believed. Magneto temporarily crippled his son's legs, leaving him out of the conflict to come.
Quicksilver's time as a hero ended when Ultron, insane robot son of Hank Pym, murdered Wanda. Pietro returned to villainy and helped propogate the Banshee drug that boosted mutant powers. When Xavier and Magneto both died during the Ultimatum Wave, Pietro killed Cyclops at super speed as well when he called for human-mutant unity. Quicksilver's Brotherhood was reformed, and he tried to play humans and mutants against each other for his own benefit. He also learned that Jimmy Hudson, son of Wolverine, shared the same mother as he and Wanda, leading to an antagonistic relationship. Several forces attempted to manipulate Pietro over time by posing as resurrected incarnations of Wanda. The last of these was a female Kang, who mortally wounded Quicksilver when he learned the truth in order to confiscate his Infinity Gem.
Quicksilver of the Ultimate Universe seemingly survived, however, and has appeared on Earth-616 as part of the New Marauders controlled by Miss Sinister and Mothervine.
In the future timeline called Earth X, Pietro died among his fellow Avengers when they fought a rampaging Absorbing Man, him having absorbed the power and persona of the Avengers‘ arch-
enemy, Ultron. One of the few Avengers left, Iron Man experienced a severe case of survivor’s guilt, and eventually tried to replace his deceased teammates with robot replications of them. Called the Iron Avengers, this series of robots looked like the fallen Avengers (Wasp, Giant-Man, Hawkeye, Quicksilver and the Scarlet Witch) and were programmed with personalities to match those of their templates. The Iron Avenger modeled after Pietro was called Bolt and, if he was destroyed, he could be easily replaced with a new model.
A time-traveling experiment gone wrong created another divergent timeline, one in which present day heroes already emerged in the 17th century, the year 1602 to be precise. Mutants were referred to as “witchbreed” and, as such, feared and hunted during the Spanish Inquisition. 
Those discovered are turned over to the Grand Inquisitor, this reality’s version of Magneto. This timeline’s version of Quicksilver was Petros, who aided the Grand Inquisitor together with his sister Wanda, a nun, both convinced that their “witchbreed” gifts came from God. In an era that had no other forms of long-distance communication other than written mail, Petros’ speed made him an invaluable asset to the Inquisitor, as he acted as a messenger between him and the King. The Inquisitor used the fervor of King James to save some “witchbreed” with less physical mutations from being burned at the stake, but eventually he and his aides were exposed as being mutants themselves. The grand Inquisitor then sought refuge with his longtime rival, Carlos Javier (who had gathered his own group of witchbreed young-sters), and entrusted him with the long-kept secret that Wanda and Petros were his own children.
Alternate realities can vary greatly and in one of them, shown in Exiles (1st series) #85-86, the genders of Magneto’s family are reversed. A female Magneto had given birth to twins, who upon reaching adulthood and manifesting mutant powers joined their mother’s Brotherhood. The female Quicksilver’s life came to end when one of Magneto’s schemes went wrong. The Scarlet Warlock was supposed to transfer Wolverine’s adamantium skeleton into Magneto’s body, but the hex 
did much, much more. Rather than simply steal Wolverine’s metal skeleton, the hex merged Magneto and Wolverine along with the rest of the Brotherhood: Mesmero, Quicksilver and the Scarlet Warlock himself. The result was Brother Mutant, an amalgamation of all five mutants. Brother Mutant was never supposed to exist and his/her presence caused a temporal disruption that caught the attention of the Timebreakers who eventually sent the Exiles to defeat and kill the near omni-potent amalgamation.