Jackson is an alternate version of Jerome Johnson, son of the second Jack in the Box, from a timeline where Jack-in-the-Box had died leaving his son an orphan.
History
After Jack-in-the-Box‘s future death, the Jackson was taken to the future by the Brothers of Trouble. There, he was trained and taught the life and words of Jack-in-the-Box. However, this mainly constited of treating Jack’s wisecracks as serious dogma. He intentionally transformed by some kind of mutation in a totally fanatic, feral version of his father.
Taking advantage of a chronal fluctuation, Jackson went back in time to meet his idol. Seeing his father didn’t follow the teachings he was taugh in the future, dissapointed, he decided to kill him with the help of the Box, another alternate version of Jackson himself. Jack-in-the-Box stopped them (with Jack freezing Jackson), but they swore vengeance on him before going back to their respective timelines, leaving the present day Jack with a dilemma to deal with.
With the eventual birth of Jerome Johnson and his choice of becoming a medic, it is most probably than the timeline than spawned Jackson has been erased.
Powers
Jackson has claws. He may or may not have some form of super agility and durability. He has veins coming out of skin, which can emit acid. However, this doesn’t seem to hurt him. he also showed a ferocity and lack of restraint on the use of violence and mortal force to even the least harmless opponent.