The Militis family, also known as the Soldier family, consists of militaristic and somewhat explosive species of the TF2 ecosystem. These American creatures often have bowl-shaped heads and are known for firing explosive projectiles at their feet in order to propel themselves into the air. This is referred to as "Rocket Jumping."
Rarely some of these creatures can get infected by parasites. The Brain Maggot to name one such parasite that can infect these creatures.
A recent scientific discovery says that the Militis family has a common ancestor with the Demolitione family (the Demoman), which would explain why they both use explosives of some form. However, the Soldiers split apart 2 million years ago, while the Demoman split away 3.5 million years ago.