The Speaker is a somewhat enigmatic character in the lore, never revealing his face and studying the Light in his laboratory in the Tower. His role is to speak for the Traveler, to interpret its messages and try to understand its will...
In-game, he is voiced by Bill Nighy. However, we are going to go for a different approach in the Arkhamverse. He will be somewhat socially awkward, not used to actually having to speak to any guests, so keep that knowledge in mind when auditioning for this role.