Old Major is the "prize Middle White boar" who had a strange dream about which he wanted to tell his fellow farm animals.
His real name is really Willingdon Beauty, but he goes by Old Major. He is quite "highly regarded," and so everyone is willing to come and listen after their daily chores are done. He has a "wise and benevolent appearance," and he calls the others "comrades," a word very much associated with Communism and the dream of equality. He describes the "hunger and overwork" that the animals endure under the leadership of Mr. Jones, the farmer, and his family, and he argues that the humans are the only creatures that consume without producing. Why then, Old Major asks, should humans rule over the animals? He points out how every group of animals on the farm contributes by producing something. Old Major convinces the animals that "All animals are equal" and that humans are the enemy, and he inspires the animals to plan a rebellion, throwing them "into the wildest excitement" with the song "Beasts of England." Then he dies just three days later.
We can interpret Old Major as a symbol of Vladimir Lenin, whose real name was Vladimir Ilyich Ulyanov (both he and Old Major are called by catchier names than their originals). Lenin served as the head of the government of Russia from 1917 to 1922 and then the Soviet Union until his death in 1924. He was a political activist who opposed Tsarist rule. When the last Tsar, Nicholas II, abdicated his power in 1917, Lenin soon rose to power. However, he died relatively soon after this (just as Old Major died after inciting rebellion), and Joseph Stalin rose to power in his place. Stalin is symbolized by the character Napoleon, and Mr. Jones, the farmer, seems to symbolize Tsar Nicholas II, an incompetent ruler who loses power.