Kenny has shoulder-length brown hair, a thin beard along his jawline, and gray eyes. He is a very tall and slim man who appears to be well-built. He has the appearance of a middle-aged man with wrinkles around his eyes, which are small and piercing. He wears a simple white shirt and black pants, along with a fedora hat.
Kenny Ackermann made a name for himself as a mass murderer, infamous for having managed to kill over 100 members of the Military Police Regiment.
He lived with Levi for a while when Levi was young. While they were living together, Kenny taught a number of battle tactics, including the strategy of always flanking one's opponent and attacking them from behind.
At some point, Kenny became the leader of a group of soldiers trained in the use of omni-directional mobility gear.
Tasked with bringing Eren Jaeger and Historia Reiss to King Fritz, Kenny and one of his subordinates begin staking out the cottage that Levi's squad is staying in, and the experiments conducted on Eren's Titan form.
The two watch as the Military Police unsuccessfully attempt to raid the cottage and detain its occupants, with Kenny commenting that Levi was able to mobilize his subordinates fast enough to avoid capture because of his training.
Kenny follows Levi's squad to Trost District, where he employs the help of some locals to kidnap Eren and Historia. Although the locals kidnap decoys, Kenny sees through the ruse and tracks down the real Eren and Historia. Seeing that Levi is keeping watch over the covered wagon that Eren and Historia are in from afar, Kenny flanks Levi and his companion Nifa in order to kill them. Although he is successful in killing Nifa, Levi anticipates Kenny's flanking maneuver and manages to survive his attack. As Kenny's subordinates kill another of Levi's companions, Kenny jovially insults Levi's small stature as he reloads his guns and uses his ODM gear to get another clear shot.
- Levi - Kenny and Levi appear to have a history together and a notably antagonistic relationship.
- Kenny is the heaviest known human character in the series, weighing 120 kg.
- Hajime Isayama has stated that Kenny's character was partially inspired by the character Trevor Philips from Grand Theft Auto V.