Jethro is not from Earth; he is of the planet Faugra, which plays a big part in the storylines, but of course I won't go much into that here. His father Malcor is a scholar and mapmaker, and one of his research projects brings him and his son to the planet Earth. Very few people know about this, as most alien landings go, but they make a few friends, including Professor Sherwood and Amber Silver.
Jethro is facinated by humans' work in fictional universes, as Faugrans generally lean toward poetry and science. He collects mountains of books, from thousand-page novels to comic books. A favorite series is the Fantastic Four, where 4 people gain new powers from exposure to radiation. Not realizing that this is completely fictional, he sets out for a nuclear power plant and breaks in (somehow) to try to gain some special power. However, the radiation fries his nerves, leaving his entire right side paralyzed.
Doctors discern that there is no choice but to amputate both his right legs. Shanu and Infinity, Jethro's mother and brother, arrive about a week later, and Shanu is horrified, as you can imagine. Infinity plays the biggest part in helping Jethro around, cracking jokes the whole time, of course. Jethro knows this is merely his way of handling stress, and is extremely tolerant.
Malcor asks the Professor if he could possibly build Jet replacement limbs. He replies that he works mainly with genetics, not mechanical systems, but he had an old friend who may be of assistance: a gnarly redneck known affectionately as Old Man Bert. He lives deep in the rolling hills of West Virginia... with his primary laboritory beneath the entire length and breadth of one hill in particular, essentially being the hill. Bert can create from scrapmetal and miles of computer wires pretty much any gadget anyone could ever need.
(I have to go soon, so the rest will be reader's digest version.)
Bert builds Jethro new body parts, the family returns to Faugra a few years later, Jethro joins the Space Patrol and keeps tabs on the sector of space containing the Earth, runs into some trouble with the Teklitans (aliens that give the Faugrans a lot of trouble) and crashes to earth in Africa -- and meets the Misfit Pride. He finds an orphaned leapard cub named Jabbers and adopts her. Oh yeah, and Jabbers can turn into a hummingbird. Bye now.