Daniel Gillies and Rachael Leigh Cook Really Put a Lot of Thought into Their Son's Name

"We just couldn't settle on a name because it's such an important decision," the actor tells PEOPLE

Nobody can accuse Daniel Gillies and Rachael Leigh Cook of rushing into a name for their son.

The Originals actor, 39, said it took days after their son was born on April 4 to settle on the perfect name for their progeny: Theodore Vigo Sullivan Gillies.

“We just couldn’t settle on a name because it’s such an important decision,” the actor tells PEOPLE, explaining that he went with nicknames including “sweetheart,” “raisin” and even “calcified alien” in the interim.

The couple had it narrowed down to two names before birth — after compiling individual lists that included upwards of 700 names to start, then creating a sort of “Venn diagram” to see which names overlapped between them, before coming up with their top choices.

“Even after he was born we couldn’t determine whether or not he was Theodore or Vigo, because he was just so beat up from [being born],” he says. “Some might say he should be Vigo because of Viggo Mortensen, kind of battle-scarred. But there was something so adorable about him.”

After much discussion, their son was given each of them — with a bonus name thrown in for reasons that would make numerologists proud.

“In the end, he got both names: Theodore, Vigo, and my wife likes Sullivan,” he says. “He was born on the fourth [day] of the fourth [month], and I said, ‘Let’s give him four names. Four seems to be his number.’ ”

Even though his name has been officially chosen, Gillies says the nicknames remain: “We call him Zoolander — he has these really pouty lips. It’s really [funny] because they don’t come from Rachael or me.”

This isn’t the first time the pair were meticulous about names. Gillies said their 22-month-old daughter had been around for more than a week before they finally settled on her name: Charlotte Easton.

“I’m amazed that people name their children before they meet them. What the hell is that?” he jokes. “Because your kid bring so much wisdom.”

— Kathy Ehrich Dowd with reporting by Caryn Midler