The Big Bang Theory has been on for so long that some not-famous guest stars early in its run have gone on to win major awards and star on shows that are almost as big as The Big Bang Theory. Here are 10 guest stars that even superfans might have forgotten appeared back in the day.

10. DJ Qualls. The ubiquitous character actor showed up way back in Season 1 as Toby Loobenfeld, a guy Sheldon (Jim Parsons) hired to play his drug-addicted cousin as part of an elaborate lie to get out of seeing Penny's (Kaley Cuoco) play. It's been long enough, and his part was small enough, that he should come back as an entirely different character, Law & Order style.

9. Steven Yeun. Before he was Glenn on The Walking Dead, Steven Yeun appeared in a flashback in a Season 3 episode as Sheldon's roommate, who was moving out when Leonard (Johnny Galecki) came to look at his room. He had two lines: "Oh, I bet you're here to check out the room for rent," followed by "Run away, dude." So if Sheldon had gotten along with Steven Yeun, The Big Bang Theory would have never existed. Imagine that.

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8. Octavia Spencer. Before she landed her Oscar-winning breakout role in The Help, Spencer was a hard-working Hollywood day player. One of her jobs was a small role as a harried DMV employee in a Season 2 episode. She went on to have a much bigger recurring role on another Chuck Lorre show, Mom, after she won her Oscar.

7. Lance Barber. This is a fun one. Barber appeared in a Season 5 episode as Leonard's high school bully. He's currently playing Sheldon's father on the Big Bang prequel Young Sheldon. So in the Big Bang Theory universe, Sheldon's dad looks just like Jimmy Speckerman, who used to stuff Leonard inside of a backpack.

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6. Eliza Dushku. This Buffy star appeared in a Season 4 episode as an FBI agent doing a background check on Howard (Simon Helberg) for a security clearance. She interviewed the guys about whether Howard was a responsible person, and Sheldon told her he once pranked him by changing his World of Warcraft character from "Sheldor" to "Smelldor."

5. Joshua Malina. In the years between The West Wing and Scandal, Malina appeared in a handful of episodes as Dr. Siebert, the president of Caltech. He hasn't been mentioned since Season 7, but he's presumably still the head of the university, so maybe Sheldon will get another angry phone call from him someday.

4. Katie Leclerc. Before Leclerc was a lead on Switched at Birth, she was Raj's (Kunal Nayyar) girlfriend in a Season 5 episode. Fun fact: Leclerc one of three actresses to appear on multiple episodes of Switched at Birth to play one of Raj's girlfriends; the others are Tania Raymonde and Laura Spencer.

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3. Josh Peck. The former Nickelodeon star appeared in a Season 7 episode as Jesse, the sleazy owner of Capital Comics, Stuart's (Kevin Sussman) biggest local competitor. Unlike Stuart, he's handsome and successful, but at least Stuart has friends...that he would trade in a heartbeat to be as handsome and successful as Jesse.

2. Max Adler. Yet another actor who was on both Big Bang and Switched at Birth is Max Adler, who appeared in a Season 8 episode as a guy who worked as a chained-up zombie in an escape room who struggles to find a balance between being scary and managing the business.

1. Charlie Sheen. Back when The Big Bang Theory started, TV's biggest comedy was Two and a Half Men. So when Charle Sheen appeared in a Season 2 episode, it was a big deal and gave Big Bang a boost. It feels like a thousand years ago that a Charlie Sheen cameo would have been a good thing, doesn't it?

The Big Bang Theory airs Mondays at 8/7c on CBS.

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