Superman's S shield is one of the most recognizable logos in pop culture since ti first arrived in 1938. It had basic beginnings being only an "S for Superman," but it soon came to hold multiple meanings from being the House of El family crest, being designed by Jonathan Kent, and being a symbol meaning hope on Krypton.
With the recent conclusion of Batman V Superman: Dawn of Justice, it is worth looking at other characters who have worn the symbolic S. While Henry Cavill has revealed he will be in Justice League: Part 1, it is possible that after the events of Dawn of Justice some other character would step up to wear the Superman emblem.
Steel's real name is John Henry Irons (named after the African American folk hero, John Henry). Once a weapons engineer at AmerTek Industries, he left that job after a weapon he created fell into the wrong hands and was used to kill people. He faked his death, moved to Metropolis and began working a construction job. One day he fell from a skyscraper and was saved by Superman. Asking how he could show his gratitude, Superman simply told him to "live a life worth saving." During the fight against Doomsday in the Death of Superman storyline, Irons attempts to help Superman fight Doomsday by grabbing a sledgehammer, but is knocked unconscious. Upon awakening, he discovers Superman is dead and gangs are working unopposed. Irons dons a suit of powered armor in Superman's memory and works to stop the gang wars and attempt to keep the peace in Metropolis. Steel never claimed to be the "true Superman," but proved to be a formidable hero.
Supergirl's real name is Kara Zor-El and the biological cousin of Superman. There have been many versions of Supergirl and different origins. We'll focus on the New 52 version, as it is the most recent. Kara's ship lands in Smallville, Kansas, but goes through the Earth and ends up in Siberia. She has no memory of the destruction of Krypton and believes it has only been three days since her ship launched. She meets Superman and learns of the fate of Krypton. Later, she travels through a wormhole to Argo City, which orbits around a blue sun. She is attacked by a Worldkiller and when its plan is to enslave Earth, Supergirl defeats them and adopts Earth as her new home.
Eradicator is an ancient alien technology discovered on Krypton. The sole mission of Eradicator became to preserve the ideal Kryptonian culture by eradicating others. Superman runs into Eradicator on Warworld and takes it back to Earth. Upon learning that its mission is to protect Krypton and is turning Earth into a new Krypton, Superman shuts down Eradicator.
After Superman dies at the hands of Doomsday, the Eradicator was regathered in the Fortress of Solitude and creates a body from the residual sun radiation from Superman's corpse. This causes Eradicator to believe itself to be Superman, although he has no heat vision, but can shoot energy from his hands. Instead of absorbing the sun's radiation to power himself, he taps into Superman's reserves and uses him as a conduit for solar radiation. Superman returns and Eradicator absorbs all the energy from the Fortress of Solitude and joins with Superman to fight Mongul and Cyborg Superman, who is attacking Metropolis. Eradicator is seemingly killed during the battle, but merges with Dr. David Connor while he is being examined at Star Labs.
We'll focus on New 52 origins once again. Bizarro was an attempt by Lex Luthor to combine Superman and human DNA. We all know mixing human and Kryptonian DNA isn't good, and the result is a mirrored version of Superman. Instead of heat vision and freeze breath, Bizarro has freeze vision and heat breath. While commonly an antagonists, Bizarro has on occasion been friendly and means well.
Not a young Clark Kent, but Conner Kent, also known as Kon-El. Superboy was a clone project by Cadmus to create a clone of Superman. He was grown in a week and his powers are given by means of "tactile telekinesis," which means he shares many powers with Superman, but not all of them. Superboy wanted to be Superman and demanded to be called Superman. However, upon Superman's return in the comics, he gave up the claim to the Superman name. Superman mentored him and gave him the Kryptonian name Kon-El.
1. Cyborg Superman
Cyborg Superman claimed to be Superman reborn and took credit for all kinds of heroic deeds. However, his true nature was revealed when he stopped Eradicator from saving Coast City and that event would eventually lead to Green Lantern becoming Parallax.
Come to find out, Cyborg Superman used to be a man named Hank Henshaw. Henshaw was an astronaut who was exposed to space radiation. His whole team suffered mutations, but his mutation allowed him to mesh with the Lex Corp mainframe where he was being treated and constructed a robotic body for himself. This proved too much for his wife to handle and she committed suicide by jumping out of a window. Henshaw ended up in space alone and blamed Superman for all his problems. Needless to say, Cyborg Superman was insane.
While these characters stepped up to have the Superman symbol, it is doubtful if any will show up in the future of the DC Cinematic Universe. It's possible, but it would be a stretch. It is interesting to know just who has worn the famous S, as Dawn of Justice proved to use a wide variety of comic book source material.