Composite Superman

History
First appearing in World's Finest Comics #142, June 1964, Joseph Meach was a driver who had fallen on hard times. In an attempt to draw publicity to himself, Meach set up a water tank on a sidewalk in Metropolis and drove off a building. Unbeknownst to Meach, the Tank was leaking, and Meach would have died if not for the intervention of Superman. The Man of Steel, upon hearing of Meach's misfortunes, obtained a job for him at the Superman Museum, where Meach was employed as a custodian. Meach's bitterness did not ubside, and being surrounded by artifacts and mementoes of Superman's career directed his anger toward Superman. One night, as Meach was sweeping in front of a series of statuettes depicting the Legion of Super-Heroes, a bolt of lightning passed through an open window and struck the display. The statuettes, which were actually miniature lifeless duplicates of the Legionnaires, unleashed an energy blast that struck Meach. Meach discovered that he was endowed with the combined powers of the Legion members. Determined to defeat Superman, Batman, and Robin, Meach used his shapeshifting power to turn his skin green and form a costume that was half Superman's, half Batman's. Calling himself Composite Superman, Meach told the heroes that if he was not allowed to join their team, he would expose their secret identities, which he learned via telepathy. The Composite Superman then created situations for Superman or Batman to handle, but which he intentionally sabotaged to humiliate the heroes. When Superman and Batman deduced Meach's evil intentions, the Composite Superman forced the team to retire or he would expose their identities. The World's Finest heroes soon discovered that the Composite Superman intent was to rule the world. Although they were unable to defeat Meach, who used his vast array of powers to keep the duo at bay, the Composite Superman was defeated when his charge of powers turned out to be temporary. Meach reverted to human form with no knowledge of his activities as the Composite Superman.

Composite Superman re-appeared a few years later, in World's Finest Comics #168 (August 1967). An alien villain named Xan came to Earth to avenge his dead father, a criminal who was captured and imprisoned by Superman and Batman. Xan studied the Composite Superman and decided to restore Meach's powers by recreating the accident that endowed him with superpowers. The Composite Superman soon captured Superman and Batman and tried to kill the team. Meach's power wore off before he could accomplish though, and soon Xan appeared explaining why he wanted Superman and Batman to die. Xan then fired a lethal energy blast at the heroes but a remorseful Meach intercepted the blast, killing him instantly.

Powers
In terms of abilities and raw power, the Composite Superman was one of the most powerful enemies Superman and Batman ever faced. The Compostie Superman possessed numerous special powers derived from various Legion members:
 * The ability to grow to giant size (Colossal Boy )
 * The ability to shrink (Shrinking Violet )
 * The ability to divide into 3 people (Triplicate Girl )
 * The ability to fire lightning bolts (Lightning Lad )
 * The ability to generate heat and light (Sun Boy )
 * The ability to make things super-lightweight (Light-Lass )
 * The ability to make things super-heavy (Star Boy )
 * The ability to eat any form of matter (Matter-Eater Lad )
 * The ability to turn invisible (Invisible Kid )
 * The ability to inflate into a large ball (Bouncing Boy )
 * The ability to stretch any part of his body (Elastic Lad )
 * The ability to shapeshift (Chameleon Boy )
 * Telepathy (Saturn Girl )
 * 12th (Brainiac 5 )
 * Magnetic Powers (Cosmic Boy )
 * X-ray vision that could see through anything, even lead (Ultra Boy )
 * The ability to phase through solid matter (Phantom Girl )

Strength Level
In addition to all of Superman's powers (derived from Supergirl), the Composite Superman' strength and invulnerability levels were three times as powerful as Superman's because Legionnaires Mon-El and Ultra Boy were invulnerable and possessed super-strength.

In other media
Composite Superman made a cameo in Justice League Unlimited in an episode called "The Greatest Story Never Told". Unlike the comic, the "Composite" is the product of a battle with the dark Lord Mordu. It's actually a fusion of Superman, Batman, and Wonder Woman with the appearance of Composite Superman, but Wonder Woman's voice, resulting from some twisted spell used in the intense magical conflict. Fortunately, the spell was undone by the time Mordu was defeated.