The Man of Steel

"The Man of Steel" is a nickname often used to describe the comic book character Superman. The title may have been borrowed from Doc Savage, one of the character's influences (and a source for creators Jerry Siegel and Joe Shuster); Doc Savage was known as "The Man of Bronze."

The Man of Steel was a comic book mini-series released in 1986, directly after the Crisis on Infinite Earths, in order to revamp the Superman universe. It was written and pencilled by John Byrne, and inked by Dick Giordano.

While the Crisis had effectively cleaned up the DC Comics universe, it was decided that Superman, DC's biggest star, needed to be "rebooted", and many of the outdated aspects of his life retconned to make him more interesting and attract more readers.

Some changes initiated by The Man of Steel from the Pre-Crisis and Post-Crisis versions of Superman:

Superman's Kryptonian biological parents' society is emotionally cold and sterile and is largely contemptous of the Terran one.
Although all of his powers remained, Superman was effectively de-strengthened; the Pre-Crisis version could easily move planets, whereas the Post-Crisis version would strain at moving a commercial plane.
The hardiness of Superman's costume is not inherent, but is due to a thin invisible aura around his body that protects material that is right against the skin from damage.
Kal-el was not an infant sent from Krypton to Earth--rather, his DNA matrix was taken from a gestation chamber, and "born" on Earth when he was discovered by the Kents.
Kal-el is apparently the sole surviving Kryptonian, with other survivors like the City of Kandor and the Phantom Zone prisoners being non-existent.
Clark's abilities developed gradually in the yellow sun environment starting with resistance to injury, then strength, X-Ray Vision and so on until he developed his flight power.
Clark adopted the Superman identity in adulthood and thus never became Superboy in his youth.
Clark adoptive Terran parents, John and Martha Kent are alive and well and Clark visits them periodically.
Lois Lane became more than "Superman's girlfriend," less interested in finding out Superman's identity; now a smart, self-reliant woman.
Superman's arch-nemesis Lex Luthor was no longer a mad scientist but a power-hungry billionaire, "the most powerful man in Metropolis," who resented Superman's overshadowing presence. (He did, however, have a number of mad scientists on the payroll and directs them much like how Walt Disney directed his creative staff's activities.)
Lana Lang and Jimmy Olsen lost all of their superhero identities.
Clark revealed his abilities to Lana just before he left Smallville and their relationship is simply a close friendship.
All of the variant forms of Kryptonite (red, gold, yellow, blue, white, et cetera) no longer existed. Only green remains.
Superman's relationship with Batman is much more tentative as each disagrees with the other's methods and attitudes.
Superman has no memory of his existance on Krypton, but instead identifies himself as a citizen of Earth.

Two of the most important changes made to Superman's personality include:

Superman's alter-ego Clark Kent was no longer "mild-mannered"; he became more assertive, and an important half of a double life; less of a front for Superman's activities.
It is not known to the public that Superman has a secret identity since he is obviously not hiding his identity with a mask.

These changes have been used to highlight the major difference between the "old" Superman and the "new" Superman. In the Golden Age of Comic Books, Superman disguised himself as Clark Kent. But in the newer, more "modern" era, it is actually Clark Kent who disguises himself as Superman.