The eldest of ten children, young Sam Guthrie was 11 years old when he became involved in a plot by the Deviants, a genetic offshoot of humanity, to improve their evolutionary status by performing experiments on children. Sam was saved by the timely arrival of the mysterious Deviant Sledge, and the minds of the children - including Sam - were wiped of the events that had transpired. Five years later, Sam's father died, and as the oldest sibling he felt responsible for supporting the family. Giving up a college scholarship, he followed in his father's footsteps as a coal miner. When Sam was trapped with a co-worker in a collapsing mine, the stress of attempting to escape triggered his latent mutant power, enabling him to blast them both free. Renegade Hellfire Club member Donald Pierce learned of Sam's powers and manipulated him into serving as one of his operatives. Pierce sent Sam into battle against Professor Xavier and his fledgling New Mutants team; however, Sam refused to kill the young heroes, instead teaming up with them to defeat Pierce. Xavier subsequently realized that Sam had been misled and invited him to join the New Mutants as Cannonball. Sam soon found himself in the role of co-leader, a position he found awkward due to his relative slowness in mastering his mutant powers compared with his teammates. He also formed a lasting friendship with his teammate Sunspot.
Later, Sam saved the life of intergalactic rock star Lila Cheney, an act that saw a romance blossom between them. During this time, Cannonball also teamed up with Spider-Man against the threat of the Incandescent Man. After the cosmic entity known as the Beyonder slew and subsequently resurrected most of the New Mutants, Sam lost what knowledge he had gained about his mutant abilities, forcing him to start learning about them over again. The encounter also left the New Mutants somewhat apathetic, and then-headmaster Magneto sought help from the Hellfire Club's presiding White Queen, Emma Frost, who enrolled them in her Massachusetts Academy and recruited them into the ranks of her Hellions. Magneto learned that he had been tricked and sought to reclaim his students, bringing him into conflict with the Avengers. After the New Mutants sided with Magneto, Frost recanted and helped restore them to their former selves. Sam's relationship with Lila eventually progressed to the stage where he asked her to visit his home and meet his family. When Lila arrived with a crystal gift for his mother, Sam mistakenly believed she had stolen it when she had actually carved it by hand. Lila left angrily, but after Sam saved her life following a plane crash, he apologized. Later, Sam and the New Mutants came to Lila's aid after she had been kidnapped by the alien Spyder. Rescuing her, Lila seemingly sacrificed her life to stop Spyder's other captives from wreaking havoc in the universe. Sam was heartbroken at Lila's apparent death. However, when she later resurfaced alive, they both realized that their romance was over as the two had moved on with their separate lives.
When the time-traveling mutant soldier Cable took over the stewardship of the New Mutants and reorganized them into the strike team X-Force, Sam learned that he was an apparently immortal mutant, one whom Cable had traveled back in time to find and guide. During a clash with the Brotherhood of Evil Mutants, Sam's blast field was disrupted by Phantazia and he was seemingly killed by Sauron; however, this manifested his apparent immortality and he returned to life. Sam eventually became romantically involved with his teammate Tabitha, a.k.a. Boomer. When X-Force were separated from Cable for a time, Sam took the reigns of leadership. He eventually graduated to the ranks of the X-Men, which placed a strain on his relationship with Tabitha. Later, the ancient mutant Selene cast doubt on Sam's supposed immortal status, posing questions that have yet to be answered. The X-Men sent Sam to spy on Graydon Creed, a presidential candidate running on an anti-mutant platform. Under cover as Samson Guthry, Sam joined Creed's campaign staff and was able to gain his trust, though Creed was soon assassinated. Returning to the X-Men, Sam soon found himself in battle against the super-strong and virtually invulnerable Gladiator of the intergalactic Shi'ar Empire's Imperial Guard who had come to Earth seeking to forcibly enlist the X-Men's help. With creative use of his powers, Sam was able to withstand Gladiator's most powerful blow and defeat him. Eventually, Sam left the X-Men and returned home to care for his sick mother. He soon encountered Deviants once more, though he had no recollection of their past meeting, and sought help from X-Force in opposing them, rejoining the team afterwards. Sam became X-Force's leader again shortly before they were called upon to aid former spy Pete Wisdom in recovering a downed satellite from Genosha, and his memories of his childhood encounter with Deviants were restored afterwards. Later, Sam asked Wisdom to help give the team a new purpose, and to that end Wisdom introduced the team to the shadowy world of black ops. After Wisdom faked his own death, Sam once again assumed leadership and continued Wisdom's crusade until X-Force seemingly died in a cataclysmic explosion. They later resurfaced, but by then a new media-savvy team had assumed the mantle of X-Force and trademarked the name. Sam went on to join Xavier's X-Corporation, a global search and rescue unit for oppressed mutants, but after a disastrous mission that resulted in the death of his teammate Darkstar, he desperately sought a fresh start. After reigniting his romance with Lila, Sam met with the weather-manipulating mutant Storm and seeing her X-Men team's role as global mutant peacekeepers as the chance he was looking for, accepted an offer to join. After Storm's team became the international, government-approved X-Treme Sanctions Executive, they moved back into Xavier's mansion. Soon after, Sam was injured in a battle against the extradimensional Fury and temporarily left the team to recuperate.
Back at the family farm, Sam was approached by Cable to rejoin X-Force to help oppose the threat of the ancient evil known as the Skornn. He declined, claiming that Cable was not to be trusted, and battled his former teacher. Defeated, Sam was then recruited into the Mutant Liberation Front by its new leader, a future incarnation of Cable's long-time ally Domino posing as the despotic Stryfe. The MLF teamed with X-Force, the feral X-Man Wolverine, and members of the Fantastic Four to oppose the Skornn, who was defeated at the apparent cost of Cable's life. Sam then joined his former X-Force teammate Siryn and the merc-with-a-mouth Deadpool in locating Cable, finding his essence scattered across various alternate Earths. They collected it and returned to their own Earth where the mutant techosmith Forge was able to restore Cable.
After M-Day, Sam returned to the mansion, shocked to find that his sister Melody had been depowered. Recently, Sam joined Rogue's strike team after Serafina, one of the hyper-evolved Children of the Vault, entered his mind and made him believe that they were married and had a family. Sam was severely upset by this psychic violation, though soon resolved his feelings after defeating Serafina.