Kermit the Frog, arguably Jim Henson's most famous Muppet creation, was the star and host of The Muppet Show, played a significant role on Sesame Street, and served as the logo of the Jim Henson Company. He continues to star in Muppet movies and make numerous TV appearances.
Friends:
Miss Piggy
Lew Zealand
Statler (sometimes)
Waldorf (sometimes)
Scooter (Muppets)
Enemies:
Scooter (Robot Chicken)
Constantine aka Worlds Dangerous Frog
Long John Silver