I once played a cowardly PC, and designed him that way on purpose, because my son was building a Skylanders-based D&D game to introduce my nephew (who was 10 years old at the time) to RPGs, and we decided we'd be running a two-player campaign where my nephew was the main character and I was the sidekick. My PC, a humanoid crow named Sam Crow, was a ranger/rogue and an absolute coward, whose battle cry upon seeing danger was, "Let's get out of here!" But that's when my nephew's PC, a humanoid sheep baabarian/cleric named Baabby, would rush into battle and Sam would be forced to follow along, because he knew deep down the safest place to be was standing right next to the hulking Courageous Sheep of Legend.
That whole campaign was me keeping Sam in the background so Baabby could have the spotlight. When it came time to pick my ranger's animal companion, for example, I went with a snail, who pretty much did nothing but sit on Sam's shoulder. But it worked: soon thereafter, my nephew joined our regular D&D game.
Johnathan