The arrogant, handsome intern who we first got to know as the man's man, both repulsive and irresistible to Izzie. The two had an on-again, off-again relationship that ended as Alex got caught sleeping with a nurse - in an attempt to regain confidence after "performance anxiety" problems with Izzie.
A former wrestler at the University of Iowa, he often tries to act more tough and aloof than he actually is. He and George O'Malley often clash due to their different personalities and also because Alex indirectly gave him syphilis (in Season One, George dated and slept with Olivia, the same nurse that Alex shagged).
After he and a visiting surgeon (Mark Sloan, the former best friend of Derek and lover of Addison) discussed his career prospects, Alex expressed interest in becoming a plastic surgeon. He gets that chance in Season Three, when Mark becomes a member of the staff - and makes Alex his personal lackey.
That means Alex Karev gets to know more about coffee than surgery. But he takes refuge on the "vagina squad" with Addison Montgomery, another attending who starts to fall for him before he turns her away. Later, he almost falls for a patient with a case of amnesia, but can't bring himself to commit to her either.
Will this patient - Rebecca Pope (also known as Ava, or Jane Doe) be the one to bring Alex Karev out of his shell at long last?
Izzie: They tried number 9? Who does 9?
Sadie: Well personally I'm a fan of 5, 7, 8, pretty much 12 through 20.
Meredith (laughs): I would try 15.
Izzie: Don't. Don't try 15. I would try 16. Yeah. I've never done that before.
Alex: You'd try 16?
Izzie: Uh huh. I would. I totally would. (Izzie and Alex look at each other then quickly leave the table)
Lexie: Um, don't do 16 too fast. It can hurt badly ... I heard.
Lexie: [narrating] Grief may be a thing we all have in common, but it looks different on everyone.
Mark: It isn't just death we have to grieve. It's life. It's loss. It's change.
Alex: And when we wonder why it has to suck so much sometimes, has to hurt so bad. The thing we gotta try to remember is that it can turn on a dime.
Izzie: That's how you stay alive. When it hurts so much you can't breathe, that's how you survive.
Derek: By remembering that one day, somehow, impossibly, you won't feel this way. It won't hurt this much.
Bailey: Grief comes in its own time for everyone, in its own way.
Owen: So the best we can do, the best anyone can do, is try for honesty.
Meredith: The really crappy thing, the very worst part of grief is that you can't control it.
Arizona: The best we can do is try to let ourselves feel it when it comes.
Callie: And let it go when we can.
Meredith: The very worst part is that the minute you think you're past it, it starts all over again.
Cristina: And always, every time, it takes your breath away.
Meredith: There are five stages of grief. They look different on all of us, but there are always five.