Rosencrantz and Guildenstern Are Dead
There are, really, two protagonists, but since Guil is the dominant personality, we've assigned Ros to be his sidekick. Not only does Guil get the most stage time, but he is also the character that the audience is likely to most sympathize with. The fact that he loses all his coins in the first scene might establish this right away. Both he and Ros spend a lot of time just watching the action in the play (like the audience), but he's the one that is always trying to interpret and figure things out. Since the audience already knows how the play will end when they come in, they must, like Guil, be in it for something more than just the action.