Back before the fail-safe was developed, human modification was done under extreme security measures. Like, in a secret overseas research base in Guantanamo, on disappeared prisoners extracted from death row. Because if the research subjects ever escaped, there wasn't much to do about it.
“Skullface” aka “Cadaver” is (perhaps the only) one who did escape.
An early experiment in Metabolic Enhancement, Skullface is very strong, very fast, but has a few glitches that give him both a skeletal appearance (think muselmann) and causes him to shut-down into a death-like hibernation if starved for enough time. Basically, his metabolism oscillates wildly without much regulation, so when pumped up on fuel (food), he can go much faster and burn much brighter than modified people with later, safer versions of this modification.