Who invented the first tank?

Australian civil engineer Lance de Mole designed a "tank" in 1912. It was submitted to the British war office in 1912 but ignored. He was finally recognised and compensated for his work as the inventor and pioneer of the mark 1 tank by the British Royal Commission on Awards to Inventors.

BUT . . .

This is always a difficult question.
De Mole certainly did design a vehicle that closely resembled (and was in some ways superior to) the Tanks that emerged in Britain and France in 1915-16. But there are other claims for, amongst others, France (Capt. Levavasseur), Austria (Gunther Burstyn), and Russia (Vasily Mendeleev) in the decade before WWI. However, none of these was ever built.

After the start of WWI, the British and French both began building Tanks, each unaware of the other's project. In Britain the most significant figures were Sir Eustace Tennyson d'Eyncourt, Major Ernest Swinton, and Willliam Tritton. It was Swinton and Tritton who jointly designed and built the prototype that became the Tank Mark I. In France, the likeliest candidate is Colonel J.B.E. Estienne, who had plans drawn up and persuaded the military to build them. The French and British projects were neck-and-neck, beginning in 1915, although it was the British who first used Tanks on the battlefield, on September 15th, 1916. The French first used their own in April, 1917.