Echo Echo is a silicon-based life form known as a Sonorosian from the planet Sonorosia (from the word "sonoros" in Galician, meaning "sound").
He is a small white alien whose body is a living amplifier, a square appendage resembling an MP3 player behind his back with a port on it decorated with a binary digit situated like the number 10, and what looks like cassette tapes on his lower legs. He can scream at ultrasonic frequencies capable of overloading machinery and stopping projectiles in mid-flight. He also has the ability to duplicate himself like Ditto, but different in that the clones are not linked in any way and can revert even if all duplicates are not re-integrated, which splinters the original's personality. With these skills, Echo Echo can create a "Wall of Sound", where he and his clones can redirect projectiles back to their source by bouncing them off of strategically placed clones. He can also use echolocation, and can channel vibrations to enhance his power. He can also transmit sound waves through speakers. The first time he appeared was "Ben 10 Returns: Part 2" to fight the Forever Knights' dragon robot, Dwayne McDuffie confirmed its Ben favorite alien, in Ben 10: Alien Force.
As Ultimate Echo Echo, he is a blue, taller, and more robotic version of himself with green eyes and black lines on his body. In this state, Ultimate Echo Echo is unlike his regular form, he cannot duplicate himself anymore (As confirmed on the Cosmic Destruction site and Dwayne McDuffie), but this limitation is well matched with incredible new abilities, can now shoot sonic screams and sonic waves from discs instead of from his mouth, these discs are on many parts of his body, that can be throw and controlled, also he can fly with the projection of sound waves, and faster than Jetray. Ben used Ultimate Echo Echo on first time in "Map of Infinity" to fight the Necrofriggian Guardians, and to help Gwen and Kevin with the traps of the temple.
Echo Echo appears as a playable alien form in "Ben 10: Alien Force The Game (Only on DS version), "Ben 10 Alien Force: Vilgax Attacks", "Ben 10 Alien Force: The Rise of Hex" and "Ben 10 Ultimate Alien: Cosmic Destruction" with also Ultimate Echo Echo.