Drizzt Do'Urden is a drow and is a great hero in the Forgotten Realms. The party can meet him when they are visiting a area close to Beregost. He is then ambushed by a large group of gnolls, but he demonstrates his amazing abilities by killing many or all of them without taking any damage. This character can be killed, but this is extremely hard to accomplish, and will cause a serious drop in Reputation. If you do manage to kill him, he will drop some items which are extremely powerful.
In Baldur's Gate II, the first time you travel between areas after escaping the Underdark, you will meet Drizzt. You can ask him for help against Bodhi. Should you get help from him, he and his companions will be waiting in the north-east corner of the Lower Tombs.
He also appears in the City of Caverns as an illusion created by 2 imps for their riddle game.