Drizzt's most faithful companion, is the feline Guenhwyvar. This cat is not just any cat, she is a magical being from the astral plane.
She was created when Anders Beltgarden wanted to make a figurine like the one his mentor had, on one of a panther. He had a craftsdwarf make a figurine and was going to give it to his good friend Josidiah Starym.
Josidiah refused the offer because of the cruelty of having to kill such a magnificent beast to have its soul trapped and inslaved.
Just as Anders was about to do the killing, his ranger heart came through and he couldn't do it. He instead let the cat go. As he did, he noticed that Josidiah was in trouble and went to help. Apparently, so did the panther. She jumped right in on top of a giant, and began raking and biting.
Anders made quick work of one, and Josidiah took out the other one. Old Whiskers (that is what Anders called her) killed the giant, but not after the giant broke her back. Knowing that she was going to die, they tried to get her back to Ander's place with the use of an extra-dimensional blanket.
Once there, as they were trying to take her out of the blanket, but realized that she was taking her last breath. Anders started to put her spirit into the figurine. When he got to the name, he went to call her Whiskers, but Josidiah said no, he named her the elven word for shadows. As he said the name out loud, he realized that that was her name, and she disappeared with the blanket into mist.
Then when he called her back from the figurine, she was already starting to heal, and because of the blanket (Anders believed) she was able to be on the material plane along with the figurine. (This is odd because the animal is supposed to form out of the figurine, not just appear near it).
Josidiah decided to take her after all, and probably had her for his entire life. When he died, (this is just my guess) the figurine was sold around, or stolen or something, and eventually ended up in a denizen from a lower planes hands, and then was given to Masoj Hun'ett.
From their it was taken from him by the Faceless One, taken back after the faceless one was killed. And then Guenhwyvar, with the help of Drizzt, freed herself from the drawl of the magic to obey her master.
Drizzt then killed Masoj, and took Guenhwyvar for himself. And Guenhwyvar has been happy ever since.
Drizzt's poem about Guen