Which character in "Animal Farm" represents Lenin?

Lenin is represented by the character (Old) Major.
As a democratic socialist, Orwell had a great deal of respect for Karl Marx, the German political economist, and even for Vladimir Ilych Lenin, the Russian revolutionary leader.

His critique of Animal Farm has little to do with the Marxist ideology underlying the Rebellion but rather with the perversion of that ideology by later leaders. Major, who represents both Marx and Lenin, serves as the source of the ideals that the animals continue to uphold even after their pig leaders have betrayed them.

https://www.ipl.org/essay/Old-Major-And-Vladimir-Lenin-Analysis-PC82XPSWG

http://www.sparknotes.com/lit/animalfarm/canalysis.html

Well, Mr. Lennon, I think Mr. Lenin may be somewhat more elusive than that. Of course it's all in the reader's interpretation.

Christopher Hitchens says, "...there is no Lenin either in 'Animal Farm' or '1984'....We have no means of knowing what Orwell intended by this astonishing omission,..."

This is on page xiii in his introduction to a 100th anniversary (of Orwell's birth) edition of the two books in one binding.

Barron's notes from their "Literature Made Easy" series says on page 11, "Major represents both Marx and Lenin,...."

Orwell introduces him thus,
"He was twelve years old and had lately grown rather stout, but he was still a majestic-looking pig, with a wise and benevolent appearance is spite of the fact that his tushes had never been cut."

Then toward the end of his laughably lop-sided speech, four rats appear, and the animals vote to count them as comrades.

The great literary critic Qp :p thinks the mention of uncut tushes shows Orwell discerned Marx's inherent cruelty, and that the admission of rats to the camaraderie indicates corruption from the very inception of the rebellion. The fact that Orwell chose the word "appearance" when referring to Major's wisdom and benevolence is not to be over-looked.

This is a mystery about which we can all have our opinions.

"Old Major – An aged prize Middle White boar provides the inspiration that fuels the Rebellion in the book. He is an allegorical combination of Karl Marx, one of the creators of communism, and Lenin, the communist leader of the Russian Revolution and the early Soviet nation, in that he draws up the principles of the revolution. His skull being put on revered public display recalls Lenin, whose embalmed body was put on display."

https://en.wikipedia.org/wiki/Animal_Farm

The great literary critic Qp :p modifies her above post to note that she agrees more with Spark's and Barron's notes and Wikipedia than with the contrarian Christopher Hitchens: Old Major seems to represent both Marx and Lenin. The uncut tushes would be Lenin's cruelty in instituting the brutal Cheka, forerunner of the KGB, and the displayed skull, Lenin's preserved body.

https://en.wikipedia.org/wiki/Cheka