The former Law & Order: Special Victims Unit star said that his character's motivation is "the rightness of his cause".
"His unbending drive to get what he wants," Meloni told The Hollywood Reporter of Roman.
"I think on the outside if you're with him, you agree and you want to follow someone like that," he continued. "If you disagree, then you think he's a fanatic."
The 51-year-old confessed that he was surprised that his character is such a child despite being one of the oldest vampires in existence.
"You know who acts like that? A child," Meloni said. "And I thought that was what kind of funny about it. Here you have this very impressive entity, yet underneath it all, he's a big old baby."
The actor previously revealed that Roman and Russell Edgington (Dennis O'Hare) will be rivals on the HBO series.
True Blood airs on Sundays at 9/8c on HBO in the US. It will air on FX in the UK later this year.
Watch a True Blood season five trailer below: