Piotr Rasputin, better known as Colossus, is one of the most instantly recognizable and physically imposing of the X-Men. Not only does Rasputin provide some muscle for the team, but he is one of the most dedicated team players around, and he has been since he was created by Len Wein and Dave Cockrum in Giant-Size X-Men #1.
With a heart even bigger than his massive metallic muscles, Piotr Rasputin has used his massive frame to help those in need on countless occasions, frequently to his own detriment. His readiness to put himself between his friends and danger has made him a beloved hero. It doesn't hurt that he can hold his own against the likes of Juggernaut and the Hulk, either. While most prominent physical feature of Colossus is his metal skin, but there's so much more to his powers and how they work with his body to make him one of the X-Men's strongest members.
1) What Is Colossus Made Of?
Colossus' most famous power is his organic steel skin. It makes him amazingly durable, bulletproof and increases his physical strength. His increased structural integrity, coupled with his immense strength allows him to lift a remarkable amount of mass. The metal comes from a psionic analog to osmium, which exists in another dimension. It is an incredibly dense metal able to deflect most weapons.
However, adamantium, like the kind on Wolverine's claws, is able to damage Colossus. Vibranium has a more worrying effect on him, as if it penetrates his body, it can revert him back to his regular form. Colossus can also still have his limbs broken in his metal form, as evidenced when Nimrod broke his arm during the 2010 crossover, X-Men: Second Coming.
2) Does Colossus Need to Breathe?
When Piotr is in his metal form, he no longer needs to breathe. This makes him far more versatile than you'd think. Since he doesn't need to breathe, he can survive in atmospheres without oxygen, traverse the bottom of bodies of water and even survive in space for a short while, but not indefinitely. This is likely due to the other effects of a vacuum still affecting the structure of his body outside of breathing.
Since Colossus can remain in his metal form for days, the lack of breathing doesn't seem to be a danger to his brain if it is deprived of the oxygen it would normally receive. Without having to worry too much about breathing, he is also able to maintain peak human speed when running in this form for a while.
3) Are Colossus' Eyes Bulletproof?
Given the way that Colossus' powers work, it'd be understandable if his eyes were a weak point. However, this is not the case. Piotr's eyes also transform when the rest of his body does. They take on the properties of steel, similar to the organic steel that comprises his skin, but this steel substance behaves differently.
His eyes become nigh-impenetrable, able to withstand the impact of bullets up to a caliber of .45. On top of this, he retains his regular vision and is able to see as he would normally despite the enhancement to his eye's physical properties.
4) Does Colossus Get Fatigue?
Rasputin's physiology while in his metal form has some fortuitous side effects, one of them being his increased resistance to fatigue. This bolsters all of his other powers, from his ability to lift large amounts to his non-reliance on breathing. While he is covered in his signature organic steel, his blood and his muscles generate considerably fewer fatigue toxins than normal.
Since he's less fatigued over time, he is able to maintain incredibly high levels of physicality for days. It's not uncommon to find Colossus in his metal form when off-mission, simply because it allows him to get more things done without any physical strain.
5) Who Are Unstoppable Colossus and Phoenix Colossus?
There have also been times when Colossus' impressive physiology has been enhanced through external forces. He was once an avatar of the Chaos deity, Cyttorak, replacing Juggernaut as the dark god's earthly avatar. As the Unstoppable Colossus, he was invulnerable, all of his regular powers were supercharged and he gained a personal force-field similar to Juggernaut's as well as a healing factor. On top of this, he would transform into an unstoppable engine of demonic destruction when enraged.
He was once again supercharged when he was part of the Phoenix Five, five X-Men who were imbued with a fraction of the Phoenix Force. He became like a god, with the powers of telepathy, telekinesis, interstellar travel, cosmic psychokinesis and the ability to alter his mass. The power of the Phoenix corrupted the hero, however, and he and Magik almost killed Spider-Man as a result during Avengers Vs. X-Men. For a brief time, Colossus even wielded these two awesome upgrades together. However, Colossus' powers did not function properly for a considerable amount of time after this brief period.