Adopted by Professor Carlo Lorenchini, he was extremely intelligent even at the age of eight. Colodi lost his mother at a young age after an android assault on the facility where she and Professor Lorenchini were working on the development of the Jammer. After the death of his mother, Professor Lorenchini mostly wallowed in the loss of his wife and neglected Colodi.
Colodi is the human counterpart of the android Whale, who were both planned and "created" by Dr. Gepetto to enable the co-existence of humans and androids. It is later revealed that after Dr. Gepetto's son's memory was wiped, Gepetto attempted to sync his (human) son's brain to an android brain and transplant the brain into a human body. That human is Carlo Colodi.
Colodi is shown to be a very kind and understanding person, yet he is firm with his principles when people try to push their ideals onto him. For example, upon seeing Whale, his first response was to help her.
After the time skip, he has shown to be even more decisive. He has a fair combination of logic and emotion in his actions and is fiercely loyal to both the humans and the androids on his side.
Colodi is a small boy at the beginning of the series and dons a plain green jacket with a white hood. He is usually seen carrying a backpack outside, since he spends his time salvaging machine parts.
After the 10 year time skip, he continues wearing a jacket (again with a white hood) and long pants. After he has been made into a cyborg and therefore consists of 70% machine, he retains his appearance except he has one mechanical eye, similar to that of an android.
It has been revealed that Carlo Colodi's existence was planned and Whale must find him in order to achieve Gepetto's will. Through the Lampione Institution, Lorenchini adopted the child under the terms that they would retain his original name of Colodi. Lorenchini had unknowingly been raising the key to the inheritance left by Dr. Gepetto.
Colodi grew up with a keen interest in robotics and spent his free time either reading engineering journals or collecting scrap machine parts in the shelter to sell for an income. He does not appear to have any friends, and is mostly neglected by his father. His closest companion is Melampo, a white dog that has been with him since he was a child.
After the gas attack by the androids, Colodi barely survived and his lower body was paralyzed. He then underwent ten years of cruel physical reformation, which not only let him walk again, but also enhanced his innate fighting capabilities.
Colodi has a remarkable understanding of the function and the processes of an android. On several occasions, he provides insight that would normally be impossible for a boy of his age. Other characters have expressed their astonishment at his abilities and intelligence, especially after knowing that he was reading robotic engineering journals at the age of eight. After the time skip, his body is 70% machine. Due to his physical modifications, his strength and speed are on par with most androids.