Megan Fox
Sure sure sure, Transformers was her breakout movie role, but we'll always remember her as Brianna Wallace, as in the Wallace Department Store Wallaces, the twins' mean-girl foil in 2001's Holiday in the Sun. The shade, the side-eye, the snark…a star was truly born.
Michael Cera
The Superbad star had a small but pivotal role in 1999's Switching Goals, playing a spoiled kid named Taylor who was offended when the shoes salesman deigned to ask if he wanted Velcro straps for his cleats. "Maybe you should just fit me for a pair of polyester sweats while you're at it." Hey, he did have a very delicate bone structure!
Jared Padalecki
The Gilmore Girls fan-favorite ditched small-town living in Stars Hollow for a trip to the big city in 2004's New York Minute. Padalecki played Mary-Kate's love interest Trey, the son of a senator, naturally.
Ethan Peck
Let's hear it for the accent work displayed by Peck—the grandson of legendary actor Gregory Peck—in 1999's Passport to Paris, which was a big freakin' deal because it featured the twins' first onscreen kisses. Sure, they were more, like, uh, pecks, but that was fitting as Peck was a then 13-year-old MK's first.
"I had no awareness for celebrity and what it would mean to be a young celebrity's first on-screen kiss," the Star Trek: Strange New Worlds actor said in a 2016 interview with Uproxx. "I remember being very nervous and I think they were too but we were all in it together."
Peck played Michel, a French flower delivery boy who had dreams of being a musician, but his dad's hopes that he would follow in his footsteps and become a butcher were harshing his mellow. Meaty stuff for the then-13-year-old's first big role.
Elizabeth Olsen
Never forget that Elizabeth, who is one of the biggest stars in the Marvel Cinematic Universe right now thanks to Disney+'s WandaVision, was the subject of the iconic "B-U-T-T Out" song from The Adventures of Mary-Kate & Ashley: The Case of the Thorn Mansion. Iconic little sister moment.
Troian Bellisario
The Pretty Little Liars star landed her small role in Billboard Dad because she was IRL besties with the Full House stars. Talk about living every millennial woman's childhood dream.
"When I was 5-years-old, my best friends were Mary-Kate and Ashley Olsen because we lived across the street from each other," she told Seventeen in 2011. "I just knew them as the girls across the street. And I remember the first time I was playing with them and something happened and I realized these aren't normal kids. They're treated differently."
Jason Clarke
Known for his dramatic work in critically acclaimed films such as Zero Dark Thirty, Dawn of the Planet of the Apes and First Man, Clarke's time as a thespian began with his role in 2000's Our Lips Are Sealed. While his character Mac was initially a villain, he comes a friend to the girls after they give him relationship advice. Also, random observation: The movie was set in Australia, yet the Australian actor used an American accent.
Willie Garson
Sometimes, we like to think Garson's turn as FBI agent Norm in Our Lips Are Sealed is actually the reason Stanford Blatch was MIA from episodes of Sex and the City, with Carrie's BFF secretly living a double life.
Tom Amandes
The Everwood actor was "cool to the Max" when he played the sisters' eligible bachelor of a father in 1998's Billboard Dad.
Eric McCormack
Speaking of hot dads, the Will & Grace star played Mary Kate and Ashley's father in Double, Double Toil and Trouble, their classic 1993 Halloween movie.
Austin Nichols
"Everyone's got a hobby, right? You're mine."
Griffen Grayson, The Walking Dead and One Tree Hill star's alliteration-loving character in Holiday in the Sun, was living easy, breezy in the friend zone with Mary-Kate's Madison until she discovered he was coaching the hot guy she was casually seeing, via head-pieces, cue cards, etc. Only after their ruse was discovered did he finally reveal his years-long obsession with her. Not weird at all!
Theo Rossi
Before he was running with a biker gang on FX's gritty series Sons of Anarchy, Rossi was competing alongside the twins in their final straight-to-video movie, 2003's The Challenge. We imagine they were very comparable experiences.
Jesse Spencer
"Need a tour guide?" Every Olsen twins fan definitely swooned when Spencer, pre-House and Chicago Fire fame, courted Mary-Kate as James, the son of a British diplomat, in Winning London. That accent!
Rhea Pearlman
OK, so, in 1992's To Grandmother's House We Go, the Cheers star plays a robber who, along with her criminal husband (played by Jerry Van Dyke), pretend to befriend the runaway 6-year-old twins in attempt to get ransom money from their single mother. WHAT?! We have about 1 million questions, the first being how on earth did we not think this was insane when we watched it repeatedly as children?