Nuclear Man 1
There were actually 2 different Nuclear Men, who appeared in the film Superman IV: The Quest For Peace. However of the 45 minutes that were cut from the final product of the film, the footage of the first Nuclear Man was also cut.
The first Nuclear Man, was rather almost Bizarro-Like in appearance. This creation of Luthor's terrorized Metropolis's Night scene, including attacking a Night Club and frying a woman when she took a liking to him.
However this Nuclear Man was rather weak and was easily defeated & killed by Superman after a short confrontation. Luthor after collecting the remains of the first Nuclear Man, decided he needed more energy in order to create a more powerful clone. Sneaking the remains on board the Nuclear Missile horde Superman tossed into the sun, a second and more powerful Nuclear Man was born.
Nuclear Man 2
This version of Nuclear Man appeared in the film, and proved to be more than a match for Superman when confronting Superman, however the price to pay for this greater power output, was that Nuclear Man needed to be in constant sunlight, or else he would be immobile and lost all of his strength.
The Second Nuclear Man confronted Superman when Superman visited Luthor, and the two soon began to battle. A fight that was literally around the world including Metropolis, Italy, China, & New York were the main places they fought at.
At end of the movie, Superman & Nuclear Man fought in space and on the moon, where Nuclear Man would meet his demise, when Superman used the moon to block the sun's rays and de-powered Nuclear Man, and then promptly dumped his powerless form into a nuclear reactor seemingly killing the clone once and for all.
Powers & Abilities
Nuclear Man 1
In the film & comic the first Nuclear Man only showed of limited amount of strength and speed. His durability was also well below that of Superman cause the first Nuclear Man died after being kicked into a power transformer. However to regular humans he was still a deadly threat since he easily killed a woman at the Metro Night Club.
Nuclear Man 2
The Second Nuclear Man showed off the standard Kryptonian power set, and on a level that he was overwhelming Superman with his assaults. The Standard Kryptonian Power set including:
Super Strength - Locked in a physical brawl with Superman, he was virtually overwhelming Superman with unbridled fury.
Super Speed - His level of speed seems to be equal to Superman's.
Super Durability - His level of Durability seems to be on Superman's level or slightly higher.
Super Agility - Another standard Kryptonian power.
Invulnerability - Roughly seems equal to Superman's own.
Heat, X-Ray, Telescopic, & Microscopic Vision.
Freeze Breath - He froze Superman in a block of Ice.
Super Breath - After Freezing Superman, he use his super breath to blow him out into space.
Aside from that Nuclear Man also displayed powers unique to himself.
Heat Generation - Nuclear Man's body is able to generate an intense amount of heat from within. To the point that his mere foot steps were melting concrete, and metal bent and twisted in his mere presence.
Energy Manipulation - Nuclear Man can fire burst of Nuclear Energy blasts from his hands, he can also use them to enhance the damaged done by his physical strikes.
Gravity Manipulation - Nuclear Man can effect the gravity around his opponents, such as when he turn Lenny Luthor is a floating spinning top and another time causing a civilian and his car to fly up in the air. However his foe must be hit by a blue energy wave he unleashes from his hands in order for him to manipulate a person or objects own gravity.
Electricity Generation - Nuclear Man's body is able to put off an enormous amount of electricity.
Razor sharp Claws - His claws on his hands were strong enough to slice into Superman's flesh.
Death Touch - Perhaps his most dangerous trait of all is this. Once he cut into Superman's flesh he caused the man of steel to rapidly age and weaken. Only through the power of his last crystal was Superman able to reverse the damage Nuclear Man did to him.
Radiation - Giving his namesake, Nuclear Man is also a highly radioactive villain, and prolong exposure around humans could possibly kill them.
Size Manipulation - Exclusively in the comic, Nuclear Man demonstrated the ability to alter his size, easily doubling in height and mass. Superman commented that he had complete control over his atomic structure meaning he could get larger if he wanted to.
Weather Manipulation - In the comic and deleted scene from the movie, Nuclear Man cause a tornado to rage in Ohio.
Molecule manipulation: Exclusively in the comic, Nuclear Man created a atomic bomb from nothing more than atoms and his sheer will.
Magnetism - Exclusively in the comic, Nuclear Man was able with but a gesture to cause any metallic object to fly up in the sky to harm civilians and annoy Superman.
Telekinesis - Exclusively in the comics, Nuclear Man was able to move people and objects around by his sheer force of will.
In the movie, just being deprived from sunlight in the shade would render him powerless.
In the comics however, Nuclear Man was able to function just fine inside of buildings, storm clouds, and other places just fine, it was only if he was in complete darkness would he be rendered powerless.
Nuclear Man in the movie, Superman IV: The Quest for Peace, he was portrayed by Mark Pillow, in his only movie role.