Nick Offerman in "Somebody Up There Likes Me."
Nick Offerman in "Somebody Up There Likes Me."

The label "supporting actor" shouldn't only describe actors in secondary roles. All actors support the movies they're in (or, at least, they should). Nevertheless, the best kind of supporting actors aren't positioned at the center of a movie's plot but end up defining it anyway. It's not just about stealing the scene -- it's about complimenting it so the entire picture makes sense. Here are 10 unsung heroes who epitomized the art of the supporting role in movies released this year. Some of them are more familiar than others, but in each case, their prominence in the projects they appeared in rank among the best discoveries of 2013.

Nick Offerman, "Somebody Up There Likes Me"

Bob Byington's alternately touching and surreal comedy covers 35 years in the life of a man named Max (Byington regular Keith Poulson) as he falls in love with waitress Lyla (Jess Weixler) and starts a family with her. Poulson and Weixler both deliver amusingly deadpan performances, but it's Offerman who elevates the material to absurdist heights. As Max's righthand man Sal, Offerman presents himself as the humorless guru guiding Max through his various ups and downs -- when in fact the older man is the real loose cannon. Therein lies the essence of Offerman's humor: There's a wicked, chaotic sensibility lurking beneath his poker-faced exterior. "Somebody Up There Likes Me" capitalizes on that talent.

Michael Fassbender, "12 Years a Slave"

Chiwetel Ejiofor's performance as a man kidnapped into slavery is crucial to making Steve McQueen's tense period drama into a deeply personal experience. Yet it's Fassbender's icy turn as twisted plantation owner Edwin Epps that injects the movie with pervasively terrifying atmosphere that drives home the central historical argument: that slavery was an industry sustained by psychopaths.

Gerald Peary, "Computer Chess"

Film critic Gerald Peary exudes an amusing blend of sheepishness and consternation in Andrew Bujalski's hilarious black-and-white portrait of an early eighties technology conference. As professor and chess champ Pat Henderson, Peary epitomizes the movie's coy perspective on the gap between personality and intellect at heart of its man-versus-machine plot. Henderson takes on the comic role of emcee for the event, as various students' computers pair off against each other in a running attempt to highlight the strongest software. He's a guide to the burgeoning uncertainties of the digital age, when we're never quite sure if we're the slaves or the masters, and his delivery renders that question hilariously ambiguous.

George Clooney, "Gravity"

"Gravity" is chiefly a roller coaster ride engineered by Alfonso Cuarón's investment in pushing the language of cinema to new extremes. But a lot of people think that it's Sandra Bullock, as one of two frantic survivors driving around the planet after the shuttle gets smashed apart, who brings the sense of fear to life. And it's true -- she's appropriately freaked out for much of the running time. However, it's Clooney's ongoing sense of calm -- he even makes a joke about his looks as the duo hurtle toward a black abyss -- that gives "Gravity" a liveliness outside of its technological bells and whistles. The actor's suave demeanor is as much a tool as anything else Cuarón uses to make "Gravity" so remarkable: While the movie starts by pointing out that life in space is impossible, Clooney brings plenty of it to each of his lines.