"Tank Dempsey: American hero. Hand him a loaded weapon, a good woman, and something to shoot at and he is happy. Enrage him and he will rip your guts out and use them as a bandolier.
Dempsey was selected for this mission after he showed his true grit at the battle for Peleliu. Remarkable though it may seem, his unit was captured during the early raids before the main invasion, and he spent 2 weeks in a rat infested bamboo cage submerged in malarial water. Well that did not stop The Tank. After he gnawed his way through the cage, he then gnawed his way through his captors armed only with a Bobby pin and his Medal of Honor which he keeps secreted in various body cavities.
Now you know there is no before the war for Dempsey, and there is no after. There is only the legend of Tank Dempsey, and how he will win the war for the rest of us."
In the original timeline, Dempsey is a stereotypical United States Marine who is brash and self-satisfied. He uses the most explicit language of all the characters in the Zombies story arc. He thinks highly of himself and his country. Occasionally Dempsey will break the 4th wall (Talking directly to players or people in the real world). His favorite weapon is the Colt M16A1, and seems to know much about it, as explained in a quote from Kino der Toten. He also favors American made weaponry, like the Stakeout. He was a part of an experiment conducted by Dr. Edward Richtofen; alongside Takeo Masaki and Nikolai Belinski, his memories were wiped out as a result of Element 115 exposure. He also become the first member of the three to regain his memories. He helped Richtofen's scheme to control the zombies as he did not know Richtofen's scheme at first as with the other two. In Der Riese, Shi No Numa, Kino der Toten and Ascension; he and the other fought for survival and unwittingly helped Richtofen's plan, but he was the first to regain his memories and became suspicious of Richtofen. In Moon, all three realized Richtofen's scheme for unlimited power and attempted to stop him; first by contacting Ludvig Maxis, who was at the Griffith Station in the Moon to help them stop Richtofen. Maxis manipulated the trio by claiming that RIchtofen's link can be destroyed by launching 3 nuclear missiles to sever the link from Agartha and the Moon, however the plan was made in haste and the Earth's ozone layer became polluted, and the explosion created more zombies, and as of this, his fate is unknown, as well as the other three.
When Samantha Maxis traveled to an alternative timeline in 1918, Tank Dempsey was still deployed with the US Army in France when he was assigned to grab Dr. Edward Richtofen as a H.V.T, and was given a transport in the form of a MKIV tank; he is also aware of the circumstances of the time, where giant robots, zombies and potential foreign intervention from Russia and Japan. When met with Takeo, Nikolai and Richtofen, the three set aside their difference to survive the zombie outbreak. When meeting Samantha Maxis and freeing her from Agartha, he and the others were informed of the future apocalypse and was tasked to avert the future apocalypse. He, Nikolai and Takeo was sent to the future to the Der Riese facility, just after the future Richtofen sent Ludvig, Samantha and Fluffy to their original fates, and threatens future Richtofen to not change the future. When the alternate Richtofen appeared and shot his future self, unwittingly erasing all the future events, he lamented Richtofen's doing, but accepts it as the future needed to change.
In the alternate timeline, he is more focused to the mission, and cursed less and he is more willing to use other weapons as well. He is also quite concerned with Samantha Maxis' safety in Agartha and along with Nikolai, he is willing to save her, but will make negative comments to her if she threatens the group. As he never encountered Richtofen before and was just briefed about him, he doesn't develop the hatred that he had, but will become annoyed if he doesn't do well, but will tolerate him in the team. He will respect both Takeo and Nikolai if they fight well, but dislikes them if they don't fight well.
"November 19, 1917 It seems beyond doubt that Fritz is up to no good. Air reconnaissance suggests prototype armored weaponry is being tested in Northern France. Scuttlebutt reads like the ramblings of a mad man; strange lights in the sky... a mysterious plague... even giant metal men. I'll be at the site within the week to learn the truth with my own eyes..."
— Tank Dempsey
"April 14, 1918 After far too long waiting on the sidelines, we finally got our first taste of combat. Our actions at Belleau Wood seem to have brought their Spring Offensive to a grinding halt. We even heard talk that Fritz has nicknamed us the 'Devil Dogs', following the allround ass kicking they took... and that's fine by me. We intercepted communications suggesting that we're not the only nation to learn of the enemy's plans. Scuttlebutt is that the Russians & Japanese are looking to grab a slice of the action. Things are going to get interesting."