In Animal Farm, Napoleon shows his ruthlessness in several places, most notably in Boxer's death.
Before sending Boxer off to be killed and turned into glue, Napoleon remorselessly and ruthlessly captures command of power on the farm by chasing Snowball away. This is the first act of Napoleon's approach to totalitarianism and despotism.
After Napoleon chases his former friend Snowball off the farm, he has countless animals killed who confess to being Snowball's allies.
Though Boxer is no ally to Snowball and is clearly the most dedicated, hard-working and physically capable animal on the farm throughout the revolution, he is betrayed by Napoleon after losing his strength and ability to work.
Boxer, who has worked tirelessly for Animal Farm, suddenly takes ill. Napoleon announces that arrangements have been made to treat Boxer in a hospital in town. However, the truck that arrives to take Boxer away belongs to a horse slaughterer, and the animals erupt in a great outcry.
Forcing Snowball into exile and betraying Boxer to his death are both clear examples of Napoleon's ruthless nature.