A mouse that was first used in an experiment to increase a person's IQ
He didnt. It was a test to see if it would work on even animals.
Algernon was a mouse they did an operation on, just like Charlie had an operation. They had the dame operation.
at the end of the story
Charlie identifies with Algernon as they are going through exactly the same process. Charlie's last words are 'put some flowers on Algernon's grave in the bak yard.'