USA Today has an article about John Hannah (Batiatus on Spartacus Blood and Sand). It features a quote from Rob about casting the role:
Yet Starz and series execs initially sought "the TV equivalent of Tom Cruise" to portray Batiatus, says Robert Tapert, Lawless' husband and Sparatcus' co-producer. "Oddly enough, this was the hardest character to cast," he says. "We had other actors, including big names. But they either couldn't get around the sex scenes or the volume of dialogue. We kept coming back to John."