91. Metallo
FIRST APPEARANCE: ACTION COMICS #252 (1959) Metallo is without question one of Superman's most feared enemies, for two reason - a) he's a badass robot, and b) he's powered by a heart made of Kryptonite, the only known substance that can weaken Superman. He was a regular Joe until he was kitted out with these upgrades, which means he doesn't have to eat, sleep or even breathe in his pursuit of carnage and misery; his brain is powered by a self-generating power-source, and this provides him with the speed and strength required to match Superman's, with the added bonus of having an in-built supply of Superman's least favourite substance in the Universe. As is similar to one of Superman's other foes, Cyborg Superman (who we'll be meeting a little bit later), Metallo is able to resorb metal objects into himself, adding to his already large, reinforced form. Depending on which iteration you're reading, Metallo can also convert himself into liquid metal form much like the T-1000 from Terminator 2, changing his shell to become objects such as chainsaws and other stabbing weapons.
90. Despero
FIRST APPEARANCE: JUSTICE LEAGUE OF AMERICA #1 (1960) Despero is one of the most feared adversaries of the Justice League of America, possessing a seemingly innate disdain for them. Sure, his single-minded goal makes him pretty much a typical comic book villain, but he's also pretty iconic, even if that stature is somewhat undermined by the countless changes the character has gone through over the years. Originally pitched as a master of mind games, Despero transformed over time into a more physically imposing character, not exactly a super-genius but more a deluded, high-falutin fool who just so happens to be extremely strong. His most memorable moment is arguably his wearing the UN flag flag as a cape during a fight there, and though he's a fun villain to watch, he's far from the most threatening and intellectually intimidating.
89. Parasite
FIRST APPEARANCE: ACTION COMICS #340 (1966) Parasite is another of Superman's big enemies, given the extremely advantageous ability he has, just as his name suggests, to leech the powers from any superhero he comes in contact with. Not only this, he can absorb virtually any form of energy contained within anything merely through touching it. He has used this in the past to become not only faster and stronger, but also more intelligent, though it is worth noting that the power he saps, specifically from superheroes, does fade over time, meaning he will have to replenish the supply. Argubably his most famous moment is when he stole Superman's powers, turning Supes into a permanent Clark form, while Parasite had essentially become Giga-Superman. In addition to all this, Parasite has even shown himself capable of sensing the life energy of everything in the world, and in recent depictions, has even been able to interface with a victim's DNA, accessing their memories and inner-most thoughts.