Ford Prefect

1. Knows a lot about what's going on in the galaxy

1.1. He's one of the authors of The Hitchhiker's Guide To The Galaxy

1.2. His brother is the president of the whole galaxy

2. Comes in to the story when he meets the other protagonist Arthur Dent on his yard

3. One of the protagonist of The Hitchhiker's Guide To The Galaxy

4. Alien

4.1. Looks like a human

4.2. Acts like a human

5. He has been stuck on Earth for 15 years

5.1. He was supposed to be on Earth only for a week

5.2. He's on the Earth doing research for the Hitchiker's Guide To The Galaxy