Albert Julian "Al" Rothstein, also known as Nuklon and Atom Smasher, is a superhero appearing in American comic books published by DC Comics. Atom Smasher is known for his powers of size and density manipulation and superhuman strength.

The character made his live-action debut in The Flash, portrayed by Adam Copeland. He also appears in Black Adam, portrayed by Noah Centineo.

Atom Smasher was created by Roy Thomas and Jerry Ordway, and first appeared in The All-Star Squadron #25 (September 1983).

Thomas spoke on Atom Smasher's creation, stating that he was named after Alan Rothstein, a friend of him and his wife Dann Thomas. Albert was made Jewish for the purposes of representation, with the Thomases believing that there were few overtly Jewish superheroes. Additionally, Albert's growth-based abilities were designed to contrast with the shrinking powers of his godfather, the Atom.

The godson of Al Pratt, the Golden Age Atom, Albert Rothstein acquired his metahuman powers of super strength and control over his molecular structure, allowing him to alter the size and density of his body, from his grandfather, a reluctant supervillain known as Cyclotron. This allowed him to fight crime first as Nuklon, and then, later, as Atom Smasher. As Nuklon, Albert was a charter member of Infinity, Inc. and subsequently served in the Justice League. He was considered a dependable, but rather insecure and indecisive superhero while in Infinity, Inc. During this time he had a mohawk haircut. While in the JLA, he forged a strong friendship with fellow former Infinity Inc. teammate Obsidian.

Albert finally gets his dream and is invited to join the reunited JSA under his new name and identity, Atom Smasher. For years, Atom Smasher cherishes his role in upholding Pratt's legacy and constantly seeks to prove himself worthy to his Golden Age idols – especially when many of them became his teammates in the JSA. He looks up to the elder JSA members, but is himself looked up to by young rookie member Stargirl. When Albert's mother is murdered in a plane crash engineered by the terrorist Kobra, he becomes consumed by vengeance, nearly crushing Kobra in his hands before he is talked down by his teammate Jack Knight, who convinces him that he should not taint the memory of his mother by associating it with Kobra's murder. Not long after the crash, Albert and Metron travel back in time and force the weakened villain Extant into a position where he takes the place of Albert's mother.

When Black Adam reforms and joins the JSA, he and Rothstein develop a rivalry at first as Al refuses to believe Adam has reformed. This soon turns to kinship after Adam justifies Al's murderous actions towards Extant. Indeed, Adam comments that he thinks of Atom Smasher as the brother he never had. Encouraged by Adam, Atom Smasher grows frustrated with the JSA's moral boundaries, especially when Kobra blackmails authorities into granting his release. Albert and Adam quit the JSA after Kobra's escape.

Shortly thereafter, the unlikely duo settle each other's personal scores. Adam kills Kobra, while Rothstein kills the dictatorial president of Kahndaq, Adam's home country. Atom Smasher helps lead a team of rogue metahumans (including former Infinity Inc. teammates Brainwave and Northwind) in an invasion of Kahndaq and overthrow its oppressive regime. Atom Smasher initially fights against his JSA teammates in Kahndaq before deciding instead to help forge an uneasy truce—Adam and his compatriots can remain in power so long as they never leave the country.