No one person invented the tanks used during World War I. The design was modified from those drawn up during the 18th century.
Designs for the tank date back to the late 1700s. Richard Edgeworth came up with the design, although it really didn't take off until the development of the internal combustion engine in 1885. At that time, a tractor with a tank design was built that was capable of maneuvering across rough, muddy terrain.
The tank was not developed until 1899. At the time, it was called a motor-war car. It had an engine developed by Daimler, a bulletproof casing, and two revolving machine guns mounted on the body. This design was reinvented several times before it became the tank used during World War I.