Bottom is a common man living the city of Venice that desperately wants to be more than what he is in everyday life. When the opportunity arrises for him to perform as an actor on the eve of the Duke's wedding, he is very excited and eager to display what he believes is a great talent. Despite what he thinks of himself, he is not a very good actor. In every rehearsal with the other common actors, he tries to take charge of the situation and volunteer for every part, not to mention give others instruction on how to perform their own.
He should be played as a sincere, yet foolish, man. He has an answer for every little problem that the troop comes across when considering their performance, and almost everyone of them is a poor choice.
Bottom's big moment in the play is when he is transformed by Puck to have the head of an ass. This comedic move can be played in many different ways and leaves a lot of room open for interpretation in both costume and performance. I think that the costume should not obstruct the actor's face, so his expressions can be seen and his lines heard. However, it should be something that the audience can identify.
While he has the head of the ass, it is important to accentuate the puns that Shakespeare 
includes in the text. When Snout tells him, "O Bottom, thou art chang'd! What do I see on thee?" He has a great reply of, "What do you see? You see an ass-head of your own do you?" (3.1.104-106). This line is greatly ironic because he is not aware of his appearance and uses an insult that only refers to himself.
includes in the text. When Snout tells him, "O Bottom, thou art chang'd! What do I see on thee?" He has a great reply of, "What do you see? You see an ass-head of your own do you?" (3.1.104-106). This line is greatly ironic because he is not aware of his appearance and uses an insult that only refers to himself. If I were producing this play and looking for an actor to cast, he would have to have great comedic timing and expression. He would have to be able to "overact" with desperation but keep a sense of pride, since he is ignorant enough to believe that he is doing everything perfectly.
The first actor to come to mind would be Jim Carey. He would bring an outrageous side to the character in both the vocal and phyiscal sense. Before and after the transformation, he could inject just enough sincerity to keep him from being too over the top. As the ass head, he could go all out and include donkey sounds and movements to accentuate the transformation.
My second choice to play the part would be Ed Helms, who appears on The Office and in the film, The Hangover. He could play the part a bit more "straight" and leave the character vulnerable. He also has enough of a voice to get rediculous in his rehearsal of lines and as the transformed ass-head.
