The Most Unforgettable Guest Stars Ever on Law & Order: Special Victims Unit

Law & Order: Special Victims Unit has kept us on our toes for 17 seasons, and by now, the procedural drama is as well-known for its shocking plot twists as it is for its revolving door of celebrity guest stars. We already know that season 18--which premieres tonight at 9 p.m. ET on NBC--will feature a cameo by Vice President Joe Biden, and we're anxiously waiting to find out which other familiar faces will be walking into the precinct this year.

To celebrate the return of all-new episodes, we're taking a look back at some of the most memorable guest stars ever to grace our screens during an SVU marathon--some of them on multiple occasions, like Modern Family star Sarah Hyland. The 25-year-old actress has appeared on the series twice, first portraying a child victim in the season three episode "Repression" and later returning to the series in the role of a killer in season ten's "Hothouse." And for Hyland, each experience was unforgettable in its own way.

"The first time I was ever on the show was when I was 10, and Mariska Hargitay was just an absolute joy to work with," Hyland told InStyle this week. "My first memory of the set is actually a funny little anecdote. I was walking into the police station to get interviewed, and on the second take, I went up to the director and said, 'Hi, I'm sorry, but my character's mom says the line that we had to come straight from school--but I don't have a backpack. Shouldn't I have a backpack?' They were like, 'Oh my gosh, good catch--thanks, Sarah!' I was 10, and I just figured that I would have to put my backpack down somewhere if I came straight from school. I don't think the props guy was very happy with me for calling him out."

Credit: Eric Liebowitz/NBC/NBCU Photo Bank via Getty

In 2009, Hyland returned to the show to portray Jennifer Banks, a brilliant but sleep-deprived student who killed her roommate in what's arguably one of the most disturbing plot lines to date. "It was really one of my favorite characters I've ever played," Hyland said. "I was obsessed with Girl, Interrupted and had read the book for the first time when I was 15 years old, and I just always wanted to play a character like that. Even when I auditioned for it, I was like, 'This is my Girl, Interrupted moment, and I'm going to try and bring as much justice to it as possible.'" But playing such a mentally unstable character wasn't easy. "The audition process was really grueling," said Hyland. "Plus, I had just turned 18 and it was the first time I was on set without a guardian. So not only was it one of the most demanding roles I had ever played, but I didn't have my mom there. I was all on my own for the first time for that role in many ways--and it was a lot of fun."

Scroll down for more of the most memorable--and surprising--guest stars ever on Law & Order: Special Victims Unit.