Guenhwyvar
Onyx Figurine of Wonderous Power

Guenhwyvar is a magical being from the Astral Plane whose essence is contained within a seemingly indestructable Onyx figurine. She is Drizzt's most faithful and beloved compainion.

Guenhwyvar was created when Anders Beltgarden wanted to make a figurine like the one his mentor had. He commisioned a Master Dwarven craftsman to 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 enslaved.
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, prefering to see her roam freely as the Gods intended. As he did, he noticed that Josidiah was in trouble and went to help. Apparently, so did the panther. Guenhwyvar fearlessly 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 until after the giant broken her back.
Now that she was going to die, Anders and Josidiah 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 they 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 and he named her the Elven word for shadows. As he said the name out loud she disappeared into mist.

When she was called forth from the figurine and her home in the Astral Plane, Guen 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 accept the gift from Anders and probably had her for his entire life. When he died, the figurine was stolen or passed from one owner to another and Guen was sometimes forced to endure years at the hands of cruel masters.
Eventually, the figurine ended up in the hands of a denizen from the lower planes, and then was given to the scheming Drow, Masoj Hun'ett.

After Drizzt killed Masoj he took Guenhwyvar for himself and Guen now had a master worthy of such a magnificent beast, one who would not use her for the sheer enjoyment of seeing victims crawl in fear before being ripped apart.

If you'd like to read the actual story on how she became Guenhwyvar, read