The Valient soldiers of the Grand Army of the Republic, clones from the planet of Kamino, who were put into service for the army after being ordered by a long thought to be dead Jedi Master.

They all share the same voice, but all have different personalities, whoever is picked will need to be able to fluctuate their personalities and will be given instructions after.

The best examples to take note of are 

Dee Bradley Baker's Portrayal - https://youtu.be/DqF9MLM7IbE
                                                            https://youtu.be/ybhkV6CtBxc?t=129

and Temuera Morrison's Portrayal - https://youtu.be/Ps6bRp0wCcA?t=294