Alex Jason, aka The Enforcer, is an agent with the John Anryn Institute.
That is a "think tank" funded by a group of wealthy individuals determined to make a difference and not worried about laws or scruples or countries while doing so. They also have one heck of a scientific breakthrough which they use to help their agents keep on going.
Jason, when we meet him at the beginning of the first recorded adventure, is an author in his late 30's and not likely to get any older. Dying and in a lot of pain from advanced cancer, he knows the end is near and there is nothing he can do to stop it. Then a hologram appears before him and offers him a chance to keep living, in a way and Jason did not need much time to think about it.
The technology is the new science of cloning and the Institute's leading scientist has made advances that are spectacular. From a few cells he can grow a new adult body in very short order. Then, using a different incredible invention, the brainwaves of a person can be infused or transmitted or whatever - placed into the clone which, naturally enough being so brand new has no memories of its own. Suddenly the patient is fully alive inside the new form.
Jason's hopes were fulfilled and suddenly he was inside a new body, cancer and pain free, and in the peak of condition, able to pay the Institute back for its gift by handling missions for it. And if his new body should become severely injured or maimed, there was always another body to shift into. Two little problems existed, though.
The first was that after around 90 days, the clone body started to, well, melt. Getting back to base to pop over to a new clone became rather time sensitive.
The second was that, apparently, each transfer diminished ever so smally the brain power of transferee so this was not really a ticket to immortality but rather just a prolonging of the inevitable.
Still, for a dying man, two or three years filled with adventure, challenge, booze, and the opposite sex was pretty good deal.