King Caesar is a combination of a dog and a lion, and possibly some type of reptile. He has large clumps of light brown fur growing on different areas of his body. His skin is made up of brown scales. King Caesar has a row of gems on his head that make up a crown like shape; they most likely absorb sunlight to power the creatures mechanical parts. While King Caesar looks entirely organic, the reality is King Caesar is almost entirely mechanical, his body is shaped by metal frames and his pelvic area holds two giant energy containers, filled by sunlight that enters his head crown. King Caesar does retain some organic features, his skin and hair grow from his body, and his brain remains organic in order for the creature to retain the ability to think during battle and make choices on its own. King Caesars brain is organic but it is surrounded by a metallic structure that can reflect beam weapons from other Kaiju. In order to awaken King Caesar a direct decedent of the royal Azumi family must sing his activation song. Years later when King Caesar appeared in Godzilla Final Wars he did not need a song to awaken, which could be explained by the Xilians altering his programming so the creature could awaken whenever it felt necessary.
Godzilla vs. Mechagodzilla
Within the context of the character's fictional universe, King Caesar possesses remarkable speed, athleticism, durability and fighting prowess. King Caesar also had the ability to shoot energy back at his opponents if they shoot energy attacks into his eyes. He used this twice with great effectiveness against Mechagodzilla before the robot wisely changed tactics and used missiles instead.
The Millennium incarnation in particular displayed great lower body strength, and was able to leap high in the air and roundhouse-kick the much heavier and spiked Anguirus like a soccer ball. This was because King Caesar is mostly mechanical.
In the game Godzilla: Unleashed King Caesar was able to absorb sunlight and release it as a beam weapon, this ability was never shown in the film continuity.