Voters may want to read the other writeups.
The character's name is Minsc, a ranger. He's in Baldur's Gate 2 as well. He believes Boo is Minature Giant Space Hamster. He keeps the old soundbytes, but gets some new ones:
"A den of stinkin' evil! Cover your nose, boo; we will leave no crevice untouched!"
"Cities always teem with evil and decay... Let's give it a good shake and SEE WHAT FALLS OUT!"
If you get a high reputation, he says: "Ah, we are all heroes! You and Boo and I! Hamsters and Rangers everywhere! Rejoice!"
He's quite a useful fighter, one of the few people in the game who can use a composite longbow, and he comes with about four 'charm animal' s every day.