What characters in the book represent Joseph Stalin and Leon Trotsky?How are they similar to their historical counterparts?

Stalin and Trotsky are represented by Napoleon and
Snowball.  It is evident that Orwell wanted to create this parallel in a couple of
ways.  The first is that both Napoleon and Snowball are descendants of the legacy that
was represented by Old Major, who can be seen as a Marx/ Lenin figure.  Both Napoleon
and Snowball are "torchbearers" of Old Major's legacy and in how they seek to execute it
is where some of the greatest similarities like.  Snowball, like Trotsky, has a much
more cerebral and theoretical commitment to his aims.  He approaches the task of
leadership in a more theoretically consistent manner than Napoleon, who is more
concerned with power and the trappings of it.  Napoleon represents the leader who exerts
power on the farm for some time, similar to Snowball, and represents the consistent rule
of Stalin.  Finally, Snowball is run off at the hands of Napoleon in a similar manner of
how Trotsky was run off by Stalin.