IDW Comics
In the TMNT series released by IDW Publishing, Casey is a young college scholarship holder and a half-orphan. Upon his mother's death by cancer, his father became an alcoholic thug who would vent his daily frustration on his son. On one such occasion, Casey was saved from another violent beating by Raphael, who had at that time lived a solitary life as a street vagrant following his mutation (unaware that he had a family searching for him), and the two quickly became fast friends and fellow vigilantes until Raphael was reunited with his family. At which point Casey was introduced to and befriended the other three turtles as well.
Read more about this topic: Casey Jones (Teenage Mutant Ninja Turtles)