Krypto

Krypto is a white dog of generic pedegree with the physical abilities of Superman but the mental capabilities of an average canine, Krypto initially caused a great deal of trouble for his new master on Earth as he would scratch at a door to indicate he wanted to go out and unintentionally gouged big chunks out of the door, or inflicting grievous bodily harm when combating villains. As a result, Krypto was for some time locked away in the Fortress of Solitude under the care of one of Superman's robots. Superman has gone to great lengths to train the dog, and he now occasionally accompanies the Man of Steel on missions.

Background
Krypto was the family dog in Jor-El's household, and was used for a test flight of the rocket that eventually carried baby Kal-El to Earth. However, Krypto's rocket was blown off course and drifted in space for many years until the rocket picked up the signal from Kal-El's rocket and found its way to Earth. Krypto arrived when Kal-El was a teenager, and the two got along famously Some time later, Superman left Krypto in Superboy's care, saying that Smallville's open spaces were a better place for the dog, and that Superboy could use a friend. The new pair slowly developed a close friendship in which Krypto willingly did anything he could to protect Conner, at one time willingly attacking and being assailed by Superboy-Prime during the Infinite Crisis.

With the murder of Conner by Superboy-Prime, Krypto has been taken by Superman to his retreat at the Fortress of Solitude where the sole remaining Earth-made Superman Robot now called "Ned" watches over and plays with Krypto.

Involvement
Krypto appears at the Fortress of Solitude, fighting Brainiac's Forces alongside both Hero and Villain players.

Trivia

 * Krypto first appeared in Adventure Comics #210 (March, 1955)
 * Batman never misses an opportunity to poke fun at Krypto when Batman and Superman don't see eye-to-eye. It also appears that Krypto has taken a great liking to Catwoman, much to her immense displeasure.