He resembles a small red dinosaur/dragon creature with the ears of bat's wings.
Guilmon is very playful and mischievous and sometimes scares people
Guilmon was created by Takato by using a sketch. While Takato went down for dinner, Guilmon's sketch was scanned into Takato's Digivice and started to come to life. Takato found where Guilmon is about to be born. Guilmon then came to life. At first Takato was afraid that his creation was about to attack him, but Guilmon became friendly and the two were instantly best friends.
Digimon Data Squad