There are Digimon out there who team up with humans who help them become stronger. Some Digimon don't really care about that kind of stuff at all though, Terriermon being one of them - he just wants to hang out and be pals all day long.
So, who is this lucky person who got to team up with Terriermon? The first thing you need to know is his name, which is Chinese, since his father is from Hong Kong. There are many different ways to spell this name, but the official version appears to be Jianliang Lee, Lee being the family name. In Japanese, his first name is spelled and pronounced "Jenrya," and his nickname "Jen," but since we love official Romanizations on this page, we'll be sticking with Jianliang, or Jian for short. Just remember to read it the way it's pronounced! Jen!!
Now that we got THAT out of the way, let's talk about how Jian and Terriermon met. I briefly mentioned on Terriermon's profile page that Terriermon started his life as a computer game character - Mr. Lee, Jian's dad, once gave Jian a Digimon computer game in which he got to raise a virtual Terriermon. Jian had lots of fun playing this game, but something went wrong one fine day. One of the Digimon in the game went ballistic, and Jian would have none of it! He made Terriermon fight, and evolved him into Galgomon who joined in on the rampage. The opponent Digimon was successfully driven off, but Terriermon got hurt in the process. One of Jian's Digimon cards turned into a magical Blue Card that he used on a special card reading device made for the game, and said device turned into a Digivice. At the same moment, Terriermon passed through the computer screen and into Jian's arms as a living, breathing being.
Personality-wise, Jian is just about the opposite of Terriermon, so they balance each other out perfectly. Jian is amazingly intelligent, and while he's usually calm and collected, he tends to worry over trivial matters and spaz out quite a bit. He is good with computer stuff, and practices a type of Chinese martial arts. At some point in his life, he accidentally injured someone, and because of this, he has a tendency to blame everything on himself. He wants to avoid fighting whenever possible, but he soon came to learn that as someone with a Digimon partner, it is sometimes inevitable in order to protect the world. He can actually take down certain Digimon himself!
Jian is good friends with the other kids with Digimon, and has a big ol' family complete with three siblings. Terriermon prefers to stick with Jian at all times, because if Terriermon stays at home by himself, Jian's little sister will use him as a plaything. But not only because of that, of course! Terriermon and Jian are best friends and love each other in a way only a heartwarming Human-Digimon pair can. Being just the right size, Terriermon is usually seen riding around on Jian's shoulder or head.