99 was a clone who lived during the Clone Wars. He was malformed during the cloning process, and demoted to the maintenance crew.
During early 21 BBY, 99 befriended Hevy and helped him during he and his team's struggle to get in the army. Hevy succeeded and passed the test, and was shipped out to Rishi Moon. He was given Hevy's medal of honor and was made a promise to keep in touch. This promise was never kept, as Hevy died during the Battle of the Rishi Moon when he sacrificed himself to warn the Republic fleet of an impending Confederate invasion.
99 met the two survivors, Echo and Fives on Kamino, shortly before the Third Battle of Kamino. As the battle began, 99 went back and forth from an weapons/ammo supply room to the front lines to give weapons and ammunition to the clones, including Havoc, who he witnessed his fall to Separatist fire. He met up with Echo, Fives, Rex, Cody, and several cadets, promising to aid them in a sneak attack. He observed the droids come in one after another, and, seeing the need for more ammunition, rushed to his friend's aid. As he limped towards the supply room, however, he was shot in the back and was killed while saying how he could finally prove himself as a trooper and he would be "one of them." Echo and Fives came to the dying clone quickly, watching in tears as he uttered his final words.
The Bad Batch
99 was born disfigured, the left side of his face drooped and unable to be controlled. This disfigurement gave him a speech impediment which mostly consisted of stalling between words. He also had a hunch on his back, his right shoulder almost turned in to his back, giving him a serious problem walking. 99's head was shaved, and he wore a blue gray janitorial outfit that had a bright sash over the left shoulder.