Hannibal Fortune is an agent with T.E.R.R.A.
That acronym stands for the Temporal Entropy Restructure and Repair Agency. It is a very unusual intelligence/law enforcement organization that virtually nobody knew about. its job was the protection of the status quo in a very unusual style in that it did not exist to keep current governments in place but to keep the current time continuum as it was.
The year, for Fortune, is 2572. The place is the Milky Way galaxy. The government is the Galactic Federation made up of the 47 known solar systems and its trillions of citizens.
In 2548 a time machine was invented. By 2554, the Federation had outlawed it because of the extremely dangerous potential the device had for mischief. Four years after the ban, T.E.R.R.A. was created to go up against a very resourceful would-be galactic ruler named Gregor Malik and his sinister organizaiton called Empire.
Malik wanted to rule his planet as he saw fit and if he also could control a few neighboring worlds, so much the better. To do that, he needed to either get rid of the GF or weaken it sufficiently to keep it out of the way. Messing with a planet's timeline to change a world's government was a very underhanded and potentially effective way of doing it. And with Empire, he got together a dozen or so like minded miscreants and promised them the same power on their worlds. So T.E.R.R.A. was created to fight Malik and his crew as well as anyone who might come later.
Fortune has been an agent for 12 years but, "thanks to the illegal temporal transporter which T.E.R.R.A.'s scientists were continually perfecting, he'd logged some sixty years' experience fighting Empire". Out of the many thousands of people that T.E.R.R.A. employed, he was one of the few who were empowered to take action. Most of the others were researchers, observers, and support staff. Fortune was "Licensed to Tamper".
Assisting each of the human agents of T.E.R.R.A., and many of the observers placed in various parts of each world's history, were creatures like Webley, described as "a fifteen pound protoplasmic alien that could shape-change." Exactly which planet Webley hails from is not stated nor have I found a name for the species. What is known is the fact that the race can morph into an assortment of shapes, all keeping its mass constant. On Earth, Webley has discovered that being a cat was the most convenient because cats can go lots of place and be mostly inconspicuous. Or he can become a bird and fly. Or a small dog though he is not partial to that one. Webley is also telepathic. The relationship between Fortune and Webley, as with the other agents in T.E.R.R.A., is a symbiotic one. Webley's small size keeps him from being able to accomplish much physically but his intelligence gathering skills are terrific.
Each agent has a planet of specialty. Fortune's turf is Earth. He may or may not actually be from that planet but he has a fondness for it and it is his chosen land. He knows its history quite well which is handy because he never knows when or where he might end up.