1. Good in social situations, likes to go out to parties/bars a lot. Is the kind of person who can be thrown into a group of strangers and no matter how different they are from him, he can instantly break the ice.
2. He also likes his alone time and will often hole up in his room to sit with his thoughts, or will go off hiking/camping by himself.
3. Confident - he's very smart and has a lot of raw talent in many different areas, and he knows it. Was somewhat arrogant about it when he was younger, but has become much humbler/respectful of other people's abilities with age (he's in his mid-20s now).
4. It's taken him some time to develop a good work ethic. It used to be that he would pick up new concepts/skills/hobbies/etc. really quickly, but would only get as far as his natural abilities would take him. Once he had to start working hard to improve, he'd lose interest and move on to something new.
5. He's very ambitious and wants to succeed in a way that meets both his standards for success and society's standards for success. This finally motivated him to buckle down and try to focus on one thing rather than skipping all over the place (he's getting a PhD in anthropology now).
6. He's worried that with his current career path (going into academia) that he's not going to be doing enough to help humanity. Not that helping humanity is his chief motivator, but he admires it as a motivator in others and aspires to be motivated by a desire to help humanity (if that makes any sense).
7. He always trusts people until they give him a reason not to. Well, sort of. He can read people really well and is good at spotting (and avoiding) sketchy folk from the get-go, so I guess it's more like he trusts anyone who gets past his initial screening. He also maintains a level of detachment in all but a few of his friendships, and therefore isn't easily hurt (and sometimes doesn't even seem to notice) when people disappoint.
8. He used to be somewhat irresponsible/inconsiderate when he was younger, although not intentionally. He's very laidback and doesn't care whether people are late on him/change plans at the last minute/fail to follow through on minor promises, and as a teenager, it didn't occur to him that other people cared when *he* did these things. He's much better about not flaking out on people now that he's older and can anticipate needs that are different from his own.
9. He views humanity as being neutral, and thinks that for every good development we have there will be a bad one to counterbalance. He also thinks that being overly cynical is just as unrealistic as being overly idealistic (his reasoning being that cynicism doesn't take humanity's positive progress into account just as idealism doesn't factor in all the negative things we do).
10. Possibly in contradiction with that, he admits that deep down he is optimistic, in an almost religious faith kind of way, that humanity will move in a positive direction.
11. Isn't phased by conflict, and reacts to it with either curiosity or amusement. I've seen him respond to someone yelling at him furiously by making fun of the person for losing their temper.
Phew! Okay, that's probably enough of a list for now. There are two types I think he could be, but will wait to see what others think before saying what my theories are. If there's any more info needed, just let me know.