The mortal enemies of all heroes and specifically the Justice League. Expect to run into some of them on occasion, and feel free to suggest any I missed.
Name: Vandar Adg II
Code Name: Vandal Savage
Age: 50,000
Powers: Genius level intellect. Enhanced strength. Immortal
Race: Cro-Magnon
Name: ???
Code Name: Ra's Al Ghul
Age: 600-700
Powers: Genius level intellect. Martial arts expert. Lazarus pit heals wounds and revives from recent death.
Race: Human
Name: Lex Luthor
Code Name: Lex Luthor
Age: 46
Powers: Genius level intellect
Race: Human
Name: Slade Wilson
Code Name: Deathstroke, formerly Slade
Age: 37
Powers: Can utilize 90% of brain, beyond peak level human conditioning, master martial artist, excellent marksman & swordsman, skilled strategist, high intellect
Race: Altered Human
Name: Teth-Adam
Code Name: Black Adam
Age: 3000
Powers: Power of 6 Gods
Race: Human/God
Name: Grodd
Code Name: Gorilla Grodd
Age: 34
Powers: Psionics, super strength, agility, incredible intellect, enhanced senses
Race: Gorilla
Name: Thaal Sinestro
Code Name: Sinestro
Age: 36
Powers: Energy light constructs, flight, shielding, lasers, boxing
Race: Korugarean
Name: Orm Marius
Code Name: Ocean Master
Age: 26
Powers: Trident assisted sorcery, telepathy, energy projection, suit grants him breathing and pressure resistance underwater
Race: Half-Atlantean
Name: Klarion
Code Name: Klarion the Witch Boy
Age: Immortal
Powers: Magical constructs & spells, flight, energy blasts
Race: Lord of Chaos
Name: Wotan
Code Name: Wotan
Age: 500
Powers: Magical constructs & spells, flight, energy blasts
Race: Sorcerer
Name: Jason Burr
Code Name: Kobra
Age: 33
Powers: High intellect, advanced martial artist, strategist, cult leader
Race: Altered human
Name: Werner Vertigo
Code Name: Count Vertigo
Age: 30
Powers: Headgear induces strong vertigo in targets
Race: Human
Name: Dolores Winters
Code Name: Ultra Humanite
Age: 55
Powers: Limited telekinesis, mind control, illusions, & telepathy, hard to kill, extremely intelligent, super strength even for a Gorilla
Race: Gorilla
Name: Lawrence Crock
Code Name: Sportsmaster
Age: 55
Powers: Olympic level fitness. Hand to hand combat expert. Acute sense. Weapons master
Race: Human
Name: Albert Michaels
Code Name: Atomic Skull
Age:28
Powers: Energy blasts from skull
Race: Metahuman
Name: David
Code Name: Black Manta
Age: 28
Powers: Lethal poison darts, skilled marksman, high-tech weaponry, lasers, visor allows visibility in deep ocean darkness, fast swimmer, good combatant
Race: Atlantean
Name: Amazo
Code Name: Amazo
Age: N/A
Powers: Ability to study, store and replicate other's abilities
Race: Robot
Name: Crystal Frost
Code Name: Killer Frost
Age: 27
Powers: Ice manipulation
Race: Metahuman
Name: Doris Zuel
Code Name: Giganta
Age: 27
Powers: Size alteration, superhuman strength and durability when big, genius
Race: Metahuman
Name: Cyrus Gold
Code Name: Solomon Grundy
Age: 50
Powers: Super Strength & stamina, magical invulnerability, resurrection
Race: Altered Human
Name: Ace, Jack of Spades, Queen of Spades, King of Spades, Ten of Spades
Code Name: Royal Flush Gang
Age: Varies
Powers: Jack - Cybernetic laser eye & firearm
Ace - Robotic body enhancements gifting super strength and durability
Ten - Razor sharp playing cards
King - Laser sword & Lance
Queen - Spade tip shooting bow staff
insulated suits & card themed hover-boards
Race: All human & one cyborg
Name: Bizzaro
Code Name: Bizzaro
Age: 33
Powers: Super strength, flight, super speed (backwards), invulnerability, arctic vision, heat breath, super breath
Race: Bizzaros
Name: Nathan Prince
Code Name: Copperhead
Age: 30
Powers: Enhanced strength, contortism, stretchy tail, neurotoxin coated fangs
Race: Human
Name: Barbra Minerva
Code Name: Cheetah
Age: 30 (80 cat years)
Powers: Enhanced strength, feline reflexes, sharp claws & fangs, skilled combatant, animal senses
Race: Cheetah hybrid
Name: Eobard Thawne
Code Name: Professor Zoom/Reverse Flash
Age: 35
Powers: Identical to Flash's, enhanced intellect, criminally insane
Race: Metahuman
Name: Dekan Drache
Code Name: Felix Faust
Age: 46
Powers: Cult leader, fire mage, illusionist, summoning, basic combat
Race: Sorcer
Name: William Zard
Code Name: Wizard
Age: 42
Powers: Able to move Earth magically via cane, power glove/stone, cloak of invisibiltiy
Race: Human
Name: Anthony Ives
Code Name: Professor Ivo
Age: 53
Powers: Immortal, creator of Amazo, brilliant robotic engineer
Race: Altered Human
Name: Tomek Ovadya Morah
Code Name: T.O. Morrow
Age: 40
Powers: Is almost always an android, creator of Red Tornado, Genius level intellect, gifted robotic engineer
Race: Human