While working at a nuclear power plant, Norton McCoy was exposed to massive amounts of radiation that affected his genes. As a result, Norton's son, Henry "Hank" McCoy, was born a mutant who showed the signs of his being different from birth with his unusually large hands and feet. As a youth, Hank's freakish appearance was the subject of much ridicule from his classmates, earning him the nickname of "Beast". However, one classmate named Jennifer came to know the real Hank after he began tutoring her in biology. On the night of the junior prom, Jennifer insisted that Hank accompany her as her date, and stood up for him after he was teased.
In his senior year, Hank's superhuman agility and athletic prowess earned him recognition as a star football player. During one game, Hank easily stopped a trio of robbers who were attempting to escape across the football field. His efforts were noticed by the villain named the Conquistador who kidnapped Hank's parents in an effort to coerce the young mutant into working for him. The X-Men soon arrived and defeated the villain, and Hank was invited by Professor Charles Xavier to join the team of teenage mutant heroes and enroll in the Xavier School for Gifted Youngsters. Unable to resist the temptation of a private institution that could offer him limitless academic opportunities, Hank accepted. Hank's days were rich with differential equations, Proust and workouts in the Danger Room. A brilliant student, Hank completed his doctoral studies under Xavier's tutelage, and finally graduated from the Xavier School to take a position at the Brand Corporation as a genetic researcher under Doctor Carl Maddicks. During one of his experiments, Hank discovered the hormonal extract that causes genetic mutation and went to inform Maddicks of his findings. However, Maddicks was secretly plotting to steal top secret government documents, and Hank took it upon himself to stop Maddicks. In order to disguise his appearance, Hank took the extract and underwent radical physical changes that enhanced his agility and strength, as well as causing him to grow fangs, pointed ears, and fur all over his body. When he stayed too long in this state, Hank found he could not return to his original form. He was now a beast in fact as well as in name. At first, he tried to hide his mutation with a latex mask and gloves, but later learned to accept his new appearance.
After receiving his doctorate in genetics and being considered one of the world's experts on mutations and evolutionary human biology, despite never having earned a Nobel Prize or been invited to join the National Academy of Sciences, Hank left Brand and applied to join the ranks of Earth's Mightiest Heroes, the Avengers. Initially accepted as a probationary member, Hank soon proved his worth and was granted full membership. During his time with the team he revealed his identity to the public in the hope that his status as an Avenger would help ease human/mutant tensions.
Following a restructuring of the Avengers, Hank left and became involved with the team of adventurers known as the Defenders which he soon reorganized into a more formal and cohesive unit, bringing in his former X-Men teammates Iceman and Angel. Following the apparent death of several of the Defenders, Hank reunited with the other four original X-Men to form X-Factor, an organization that intended to seek out and aid other mutants under the pretense of hunting them down. Shortly after the formation of X-Factor, Hank was captured by Maddicks who sought to experiment on Hank in an attempt to find a "cure" for his son's own mutancy. However, the serum Hank was given caused him to revert to his original human appearance. Soon after, Hank first met television anchorwoman Trish Tilby, who was investigating X-Factor.
During an attack on New York by the eternal mutant Apocalypse and his Four Horsemen, Hank was stricken with a virus that sapped his intellect and increased his strength every time he exerted himself physically. The more Hank used his strength, the stronger he got, but the less intelligent he became. Finally, to save his friend Iceman from the deadly kiss of the mutant named Infectia, Hank intervened and was himself affected, the result of which returned him to his blue-furred form and restored his intellect. Soon after, Hank and Trish began seeing each other romantically, however her work often intruded on their relationship and the pair ultimately called it off.
After X-Factor disbanded, Hank returned to the ranks of the X-Men and became the team's resident technological and medical genius, working on everything from advanced alien technology to the deadly mutant-killing Legacy Virus. Hank also continued his on/off relationship with Trish until she released information on the Virus to the public, which caused hysteria that culminated in the beating to death of a young mutant. During this tenure with the X-Men, Hank was lured into a trap and replaced in the ranks of the X-Men by the Dark Beast, an alternate-reality version of himself. Sealed behind a brick wall, Hank was nearly about to give up and let fate win when his water tube broke and spurted, revealing the grooves of a trap door in his cell. Energized by hope, Hank broke his restraints and escaped with the aid of the new government-sponsored X-Factor team. Hank returned to the X-Men, and soon after met with Trish to apologize for his previous harsh treatment of her. She forgave him and the pair renewed their relationship.
Hank eventually took an extended leave of absence from the X-Men to work on a cure for the Legacy Virus, which he ultimately found thanks to his implementing the work of his former colleague, the late Moira MacTaggert. Soon after, Hank joined Storm's team of X-Treme X-Men in their quest for the diaries of the late mutant seer Destiny. Almost killed in the team's first battle with the villainous Vargas, Hank's life was saved by his teammate Tessa who used a heretofore-unseen power to accelerate the Beast's mutation to a new level. Hank returned to Xavier's mansion to recuperate and mutated further, becoming bulkier, heavier, and taking on a more leonine appearance. Forced to relearn fine motor control over his body, Hank once again served as the team's resident genius, as well as an active teacher of dozens of young mutants at the renamed Xavier Institute of Higher Learning.
Unable to deal with his latest mutation, Trish called Hank and ended their relationship over the phone. Soon after, Hank was beaten into a coma by Beak, who was possessed by Professor Xavier's malevolent twin Cassandra Nova, who herself had possessed Xavier's body. Hank recovered in time to expose her plans and Cassandra was ultimately defeated, but not before she had exposed her brother Charles to the world as a mutant, forever changing life at the Xavier mansion for the X-Men.