Jesse Eisenberg and Ashton Holmes: Separated at Birth?

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Did you catch Jesse Eisenberg in last week's premier episode of CW's new series "Nikita"?

Oh, wait a minute. That wasn't Eisenberg, the 26-year-old actor who starred in "Zombieland," "Adventureland," and plays Facebook founder Mark Zuckerberg in the widely-anticipated movie "The Social Network."

On "Nikita," the actor who plays Thom, a recruit assassin, is 32-year-old Ashton Holmes, a dead ringer for Eisenberg. Five years ago Holmes played the son of Viggo Mortensen in "A History of Violence." More recently, he portrayed a soldier in HBO's Emmy award-winning miniseries "The Pacific"

Jesse Eisenberg and Ashton Holmes

Although Hollywood values uniqueness, sometimes genes hold the upper hand. And on those occasions the resemblance between certain celebrities can be uncanny enough to inspire double-takes.

Angela Mickey, a casting director at Liz Lewis Casting Partners in New York, believes such strong resemblances can be a double-edged sword. If an actor is recognized and popular, she says, producers might want someone similar-looking, especially if project developers don't have the funds to afford the better-known target. Other times, she says, it may simply be a question of availability. "Jesse Eisenberg is so busy that he could well be booked for the next couple of years," says Mickey.

"The downside is there can come a point where people overly associate you with the person you look like," she says. "You may then be known as 'the less expensive version' of the actor you resemble."

Who's Who?

Ian Somerhalder, who met an untimely death early on "Lost," now stars in CW's "Vampire Diaries." His older mirror-image, Rob Lowe, appears as a state auditor in NBC's "Parks & Recreation," which resumes its run mid-season.

Ian Somerhalder and Rob Lowe

Celebrity Lookalikes

Chris Mulkey can be seen playing Boss Hague in HBO's "Broadway Empire," and earlier this year he appeared in "Saving Grace." He bears an uncanny resemblance to Patrick Swayze and, some say, Chris Cooper.

Chris Mulkey and Patrick Swayze

Don't underestimate the "kid" factor and changing facial features.

Rosario Dawson, Melonie Diaz and Lea Michele

Four years ago, in "A Guide to Recognizing Your Saints," actress Melonie Diaz played the younger version of a character portrayed in adulthood by Rosario Dawson. Today, the 26-year-old Diaz could pass as a sibling of Lea Michele's character, Rachel Berry, on 'Glee."

However, even if an actor has a doppelganger, what often cuts through the confusion is the phenomenon of several of that actor's films releasing at the same time. This sheer output of product can help audiences identify with a particular star.

"At some point, the physical similarities fade away and the personality of the actor comes through," says Mickey.

Until then, those double-takes are a fun part of celebrity awe.