Godzilla (Gojira) - The King of Monsters, radioactive dinosaur. Special features: Atomic breath, advanced healing factor, can fight on land and in the sea.
Mothra - Giant moth
Special features: Uses mandible to bite opponents, can create gales with wings, can also emit energy beams and poisonous powder.
Rodan - Airborne prehistoric reptile
Special features: Can fly at supersonic speeds, is resistant to Godzilla's atomic breath
King Kong - Giant gorilla
Special features: Semi-human intelligence and great physical strength
Gamera - Massive flying turtle
Special features: Extremely resilient shell, eats and breathes fire, can fly and has large, sharp teeth.
Anguirus - Radioactive dinosaur, similar to an Ankylosaurus. Godzilla's most trusted friend and ally.
Special features: Sharp teeth and claws, spikes all over body. Can move move fast and can burrow substantial distances.
King Ghidorah - The King of Terror. A three-headed mutant dragon.
Special features: Can emit gravity beams, fire and bolts of electricity from different heads. Has golden armour, and can produce hurricane winds.
There are others too!
I like Mothra because he looks so cute!