Who gained leadership of animals in animal farm and why?

That would be Napoleon. He was manipulative and strong willed. Napoleon, one of the three pigs who originally helped spearhead the rebellion on Manor Farm, becomes the supreme leader of the animals over time. As he is a clever pig, beyond simple intelligence, he implements education programs for the young, drives Snowball from Animal Farm, has his enemies butchered, and engages in human behavior once forbidden.