John Henry Irons built his suit of armor and donned it as the Man of Steel in the wake of Superman's death, as he felt that Metropolis needed a hero (he debuted the same time as Superboy, the Kryptonian Superman, and the Cyborg Superman, as was the only one to not claim to be the real Superman).
After the real Superman returned, John Henry shortened his name to simply Steel.
Steel was briefly a member of the Justice League.
He retired from active duty after sustaining massive injuries, but recently returned when Superman disappeared once again.
Steel's niece, Natasha, donned armor as the fourth Steel.