Dr. Tardis is not related in any way to the popular British TV show. The TARDIS is a machine that can travel anywhere in time and space. Tardis is the last name of Dr. Jonathan Tardis. His family was actually named Tirdas in the old country, but an error at Immigration caused his grandparents' last name to be changed to Tardis. Gramps didn't mind, though. "I'm in America," he would say. "What does a name matter when we're in the greatest country in the world?"
That was right before the EMP.
Today, Jon is a physics professor. He and his assisant, Terry, were working on an experiment to prove the alternate universe theory of physics. Specifically, they were trying to prove the theory that each decision, no matter how minor, creates a new universe, much like ours but with that one decision different.
After several years of trials (and failures), Jon and Terry finally built a working experimental prototype. When they turned it on, they thought they'd failed again. They merely saw the back of their lab. It wasn't until Terry approached the machine's gateway that Jon realized it had worked! The Terry in the target universe had walked around the back side of the gateway, and seeing the two Terrys, he knew he'd succeeded, and travel between universes was possible!
Unfortunately, the gateway was unstable. When Jon tried to walk through it, all of his alternate selves in EVERY universe became connected through this one, single body. Now he has millions of different time streams running through his head. Some are so similar that the differences are irrelevant, but some are very different. In some, Jon is not even human. In others, the EMP never happend. In another, the US government didn't cut off NASA's funding after the moon landing, and the development of artificial gravity in 1982 led to interstellar travel by the end of the century.
Most of the time, he seems to be a perfectly normal human male, but he will sometimes come up with weird comments about places or people he couldn't possibly know anything about. Sometimes, his awareness will slip, and he'll "take a trip", as he calls it. These fugues can last from a few minutes to a few hours. Often, when he takes a trip, he can bring an artifact back with him: whatever his alternate self was holding when the fugue ended. He's learned to intentionally invoke this "travelling" state, often with interesting results.