Buenaventura Durruti.
He succeeded in welding together 10,000 volunteers without previous military training and experience of any sort. No military brow-beating, no coercion, no disciplinary punishment was needed to hold the Durruti column at the front. They triumphed in much of Spain despite the fascist superiority in weapons and resources. The anarchist contribution was decisive in resisting the fascists throughout the country and in Catalonia defeated the rebels singlehandedly, Durruti being one of the boldest fighters.
He was a man who fought for his union and ideals; who never sought any special privileges for himself, who acted as much as he read or thought, who loved, dreamed and was determined to leave this world a better place than when he entered it. Can't say that for any other general, they were mostly one dimensional brutes.