The Teenage Mutant Ninja Turtles (TMNT) franchise has a wide array of iconic villains. Here are some of the most notable ones:

1. Shredder (Oroku Saki): The primary nemesis of the Turtles, Shredder is the leader of the Foot Clan, a criminal organization. He is a master of ninjutsu with a high IQ and has various versions including Utrom Shredder, Super Shredder, and Tengu Shredder.

2. Bebop and Rocksteady: Originally street thugs, they were transformed into mutant henchmen by Shredder. Bebop is a warthog and Rocksteady is a rhinoceros. Despite their lack of intelligence, they possess great strength.

3. Krang: An alien warlord from Dimension X, Krang allies with Shredder and provides him with advanced technology, including the robotic body he uses.

4. Foot Clan: A group of ninjas led by Shredder. They serve as the main group of antagonists.

5. Baxter Stockman: A scientist who often allies himself with Shredder and creates various inventions to defeat the Turtles.

6. Karai: A high-ranking member of the Foot Clan. She has been depicted in various roles across different TMNT media, ranging from Shredder's ally to his daughter.

7. Rat King: He has been depicted as both friend and foe of the Turtles.

8. Tokka & Rahzar: Mutated by Shredder using the same ooze that created the Turtles, Tokka and Rahzar are powerful but intellectually lacking.

These villains have kept the Turtles busy over the years, contributing to the franchise's enduring popularity.