An Italian-American mutant from Boston, Santo was sent to the Xavier Institute where he befriended Julian and the would-be Hellions. He was originally advised by Iceman, but was selected by Emma Frost to be part of her prized Hellions squad. Santo and the rest of the Hellions went on to win the Field Tournament and were declared the best squad at the end of the school year. During the summer vacation, Julian, from a well-to-do background, invited his friends to his home. The Hellions ran into trouble quickly, as his and Mercury appearances disturbed people at the airport. After a brief struggle, the group was allowed to board, and made their way to California, where Julian originates. Soon, the team encountered the 'Kingmaker', from whom they each received a trial wish. Santo's wish was to become a World-class Champion in superhuman wrestling. However, when the Hellions eventually refused a permanent deal with the Kingmaker, the Kingmaker shattered Santo with a laser blast. Julian used his telekinesis to piece Rockslide back together, and together the Hellions defeated the Kingmaker.
After the effects of M-Day, he was one of the few students who didn't lose their powers. The depowered students and staff were sent to their homes. One bus was bombed by anti-mutant religious zealot Reverend William Stryker, and Santo's former teammate and friend Brian was among those killed. The X-Men held a funeral for those students whose parents would not accept them, and Santo reflected upon how he had "failed" by not being able to save those killed. With the mutant population drastically decreased, the government sent the Sentinel O*N*E* Squad to watch over the school, which began housing as many remaining mutants as would take refuge. All of the remaining students were placed by Emma Frost into an all-out brawl, and the ones deemed to be the best were to be assigned to become a group of in-training X-Men. Santo made the team and began training to become an X-Man. William Stryker continued his terror attacks against the school. Santo's teammate Josh ended Stryker's plans by killing him. The New X-Men, with the help of David, then made the connection between Stryker and Nimrod. The team leader, Nori, then decided that the team would find and destroy the robot. When the team confronted Nimrod, Rockslide revealed how much the death of his fellow schoolmates had affected him when he intercepted an attack by Nimrod meant for Hellion crying "Not again!" He was obliterated by the attack, fueling the rest of the team in their eventual defeat of Nimrod. Hellion and Mercury tried desperately to awaken and to piece him back together, but Rockslide's remains were initially unresponsive. Thankfully, even in his shattered form, he was able to survive, and was finally put back together, only to become larger and more rugged than his previous form. Rockslide is later seen talking to Match and Anole about their abilities and how useful or useless they would be if they joined the New X-Men team, indicating Match and Anole may be possible candidates for admission onto the team. He was at the memorial service for all the students lost in Stryker's attack on the Institute. Rockslide sees the Young Avengers on television, learning about them for the first time, to his fellow students' surprise. He decides that the New X-Men should beat them up, with himself fighting Hulkling. Loa and Anole tell him that Hulkling would win. Rockslide accompanied the X-Men when they jumped from the Blackbird to save Cessily from the Facility. He helped with great enthusiasm during the fight, and in the aftermath, made fun of Shadowcat and her powers, saying that being an X-Man must be "really hard". Kitty then jokingly threatened to kill him.
Quest For Magik
Santo and the other students were captured by Belasco, and taken to Limbo. While hiding from Belasco, along with Blindfold, Match, Loa, Anole, Wolf Cub, Pixie, and Gentle, Santo was unsure what to do. As demons approached the group, Santo fought them off, but then seemingly exploded when he tried to shoot his fists at them. Santo then seems to reconstitute himself in a magma rock form that is also impervious to magic and beats the badness out of Illyana who then helps them to rescue their fellow students and kill Belasco. Back home, Rockslide threatens to quit if Pixie and Anole aren't made part of the New X-Men.
World War Hulk
Rockslide is one of the students that goes up against the Hulk when he attacks the Institute. He knocks over the Hulk so the other students can hold him down, but is knocked away when Hulk regains his strength. When Rockslide attacks him alone, it appears that Hulk knows who he is and what he can do. The Hulk rips off both of Rockslide's arms, steps on him, then tears off his legs. He then rids Rockslide of his limbs by throwing them a great distance, ridding Rockslide of his powers and the ability of ambulatory function. His limbs were eventually located after Hulk leaves.
Children of X-Men
Rockslide is seen playing pool with X-23 and Anole; he and X-23 try to convince Anole to let them cut his other arm off. After Santo calls Anole a sissy, Anole gets offended and pushes him out the window while Rockslide proclaims "I swear I didn't know! Don't be so sensitive!" After Rockslide refuses to blow himself up, Anole calls him a sissy to get him to do it. Anole then offers to try and blow up Santo himself. Beast and Colossus supervise Santo's brief training on exploding and regenerating. Santo later agrees to stay up with Indra because he is worried that he is going to die and while having an indoor campfire, Santo points out that it doesn't matter how old they are, they are mutants and someone is going to come gunning for them, and when they do he wants to go down fighting. Later, he outs Victor as gay to some of the other students, though Loa was already aware and says that everyone already knew of his orientation.
Some of the New-X-Men decide to launch a pre-emptive strike against the Purifiers. After spying on the Purifiers, they are ambushed by the Reavers; Rockslide and X-23 manage to damage Lady Deathstrike’s armor. Pixie then manages to teleport the team out and are spread between Washington and the Institute. He was later seen aboard the X-Jet with Iceman and the New-X-Men during the Sentinel attack on the mansion. Later, he is seen talking with Dust about honoring the dead. They are joined by Mercury and as they approach the cemetery they find Predator X feasting on the bodies of dead mutants much to their horror. He holds the creature back so the others can escape, knowing that he can't be killed by it, though it does make short work of him.
Santo meets up with Blindfold at a coffee shop and she tells him about her premonition of soon-to-be-formed Young X-Men squad, including the death of one of their future teammates, though he appears to take no heed. Just as predicted, Cyclops offers Santo the position, but claims that he was not planning on recruiting Ruth. Santo demands that she be added to the team, stating that Ruth's premonition included both him and her, and threatened to reject Cyclops' offer if she was not recruited as well. It is later revealed that Cyclops is really Donald Pierce in disguise manipulating the Young X-Men to attack the original New Mutants. As Blindfold predicted, Wolf Cub is killed in the final confrontation with Pierce, which impacts Santo greatly.
Santo and Mercury are watching a training session between Pixie and Nightcrawler when Pixie stabs Kurt with her soul dagger. They run in and move Pixie away from Kurt's unconscious body, Beast enters and Pixie regains her senses. When she removes her dagger, Magik's soulsword emerges from his chest and Magik teleports in ready to reclaim her sword. Rockslide takes on Illyana, thinking he is still resistant to magic, forgetting that it was only when he was composed of Limbo's terrain. Illyana shocks him by easily defeating him. After he reforms, the gathered X-Men hold a meeting and he along with Mercury are put on a team of X-Men being sent to Limbo due to their resistance to magic, but only if he reforms from Limbo rock. In Limbo, Rockslide reforms out of Limbo's terrain as the team enters Belasco's castle to assist Pixie. Finding Illyana defeated by Witchfire and Pixie transformed into a demon, Rockslide and Mercury are forced to fight Colossus and Wolverine who become magically mind-controlled.
Powers and Abilities
Geokinetic Psychic Entity: In New X-Men #42, Beast determines that given Santo's two experiences reforming his body after being destroyed, Santo is actually a non-physical psychic entity that can form and control a stone "golem". Santo has, however, lost the ability to fire "granite projectiles", and now has the power explode on command and reform himself from any surrounding rock.
Santo's body is composed completely of granite. His body is inorganic. In the Hellions mini-series, he was shattered by the Kingmaker and put back together by Julian, much like how Emma Frost was reanimated by Jean Grey in the first New X-Men series. Given that Julian's power is obviously much less developed than Jean's, it would make sense that Santo's body is designed to be pieced back together should it be broken. This is supported by the recent incident in which Santo's body was obliterated by Nimrod, only to eventually put itself partially back together (Santo needed Julian's help again to fully reform). This time his appearance is larger and more rugged. In the Quest for Magik arc, this process was undergone again. Santo being blown up again in Limbo, this time returning as a large lava/magma elemental type creature. This seems to suggest that Santo's body is capable of taking on the properties of the Earth he is in contact with. It is unknown whether this is able to be controlled or if it is a passive regenerative ability that occurs when Rockslide's body is destroyed.
- Superhuman Strength: Rockslide has continuously been shown performing great feats of strength. Rockslide possesses superhuman strength. He is capable of lifting 75 tons.
- Superhuman Stamina: Rockslide's musculature generates less fatigue toxins during physical activity than the musculature of an ordinary human. He can exert himself at peak capacity for at least several hours before fatigue begins to impair him.
- Superhuman Durability: Rockslide's extremely dense bodily tissue is considerably harder and more resistant to injury than the body of an ordinary human. He can withstand great impact forces, high caliber bullets, temperature and pressure extremes, and falls from great heights without sustaining injury.
- Rock Explosion: He can also detach parts of his body, flinging them as heavy rock projectiles. He has no control over these body parts until he reattaches them manually. Though now no longer capable of that he can only fully explode.
Combatant: Rockslide is a good hand to hand combatant.
Rockslide is capable of lifting within the class 75 range.
Energy Blasts: He can be split into pieces by powerful energy blasts from enemies such as Nimrod.
Rock Seperation: If parts of his body are ripped off and thrown very far away they will not come back.
Santo is typically depicted as superficially brash, oblivious, and inconsiderate. Originally, he was introduced as a stereotypical bully. However, he cares deeply for his friends, recalling the deaths of the depowered students, especially Tag, which usually motivates him to perform feats of incredible strength or bravery. He also has a strong sensitivity for his teammates, such as when Sooraya continued to "beat herself up" over the death of Icarus as well as recognizing that he is not supposed to see her without her abaya. He is very protective of his teammate Mercury. Santo also has a strong sense of honor, telling Anole and Pixie that he would quit the team if they were not included on the roster.
- He is a fan of the video game Dance Dance Revolution.
- Santo is considered the school bully.
- The idea of Santo desiring to be a world-class superhuman wrestler has reoccurred twice now—once in the Hellions mini-series and again in the House of M series.
- Santo is a fan of the television program Medium starring Patricia Arquette. In the same issue, he also mentions Murder She Wrote.
- He respected the Hulk and even pretended to be him, when he wasyoung, until the Hulk attacked the X-men.