General Paul Emil von Lettow-Vorbeck (20 March 1870 – 9 March 1964).
Starting in 1914, he led a relentless guerrilla campaign in German East Africa that is considered one of the most effective in military history.
With a force that never exceeded 14.000 men (many of whom were non-front line units and local porters), he managed to keep in check a force of over 300.000 British soldiers.
In November 1918, still oblivious to the Armistice that had been signed 2 days before, he captured the town of Kasama and kept advancing towards Katanga, to the south-west of his position. On the way he met a local British magistrate, who informed him of the Armistice. He then decided to surrender.
He had virtually never been defeated on the field since the beginning of the war.