You've Most Likely Seen Him In ...
...well, it depends on what kinds of movies you're watching. You've almost certainly seen Krumholtz plenty of times, but just what those movies were probably varies. My guess is that the widest possible exposure came with his performances as an elf in the Santa Clause films and as Wednesday Addams's camp boyfriend in Addams Family Values. Two sides of the same coin, really: smart, deceptively crafty nerd boys.

Unless You've Really Been Paying Attention, in Which Case You Remember Him From ...
...modestly-budgeted, critically-appreciated films like the 1998 family comedy Slums of Beverly Hills, or Joss Whedon’s big-screen continuation of his Firefly franchise, Serenity. Both movies managed to showcase Krumholtz’s ability to make an impression in either small films or with small roles, often both.

"Wait, So He's That Guy From ..."
... bigger budgeted, stoner-related type properties. He showed up in the Harold and Kumar movies and dutifully collected paycheck, while also starring alongside Michael Cera and Jonah Hill in Superbad.

You Can Also Go Back and Spot Him In ...
...Well, 10 Things I Hate About You, for one thing. He plays Joseph Gordon-Levitt’s best friend. He’s also in a pair of period indies dealing with coming-of-age teens that needed a boyish actor who read as decidedly Jewish. In the late ‘90s Krumholtz got the chance to act two auteurist visions, though one certainly more bleak than the other. He starred in Barry Levinson’s nostalgic Liberty Heights, with Ben Foster and Adrien Brody, as well as Ang Lee’s The Ice Storm, alongside Christina Ricci, Elijah Wood, and Tobey Maguire.

Perhaps Your Cultural Tastes Lie in Television, In Which Case...
... Arguably Krumholtz’s biggest exposure has come on television, via his long-running CBS math-can-solve-murders drama Numb3rs. But perhaps most notoriously, Krumholtz played a mentally unbalanced patient in one of the most harrowing E.R. episodes ever, as his character brutally stabbed Lucy Knight and John Carter and left them both for dead.

Where You Can Find Him Now ...
...Krumholtz joins a cast of stoners and actors and actors playing stoners -- including Seth Rogen, Jonah Hill, Jay Baruchel, Craig Robinson, and James Franco -- in This Is The End.

Previously: The 5 Best and 5 Worst Things We Learned About the Future From 2013 Movies