Louis Alfred Székely (; born September 12, 1967), known professionally as Louis C.K. (), is an American stand-up comedian, actor and filmmaker. C.K. has won three Peabody Awards, three Grammy Awards, six Primetime Emmy Awards, and a Screen Actors Guild Award as well as numerous awards for The Chris Rock Show, Louie, and his stand-up specials Live at the Beacon Theater (2011) and Oh My God (2013). In 2015, Rolling Stone ranked C.K.'s stand-up special Shameless number three on their "Divine Comedy: 25 Best Stand-Up Specials and Movies of All Time" list and ranked him fourth on its 2017 list of the 50 best stand-up comics of all time.

C.K. began his career in the 1990s writing for comedians including David Letterman, Conan O'Brien, Dana Carvey, Chris Rock, and Saturday Night Live. He was also directing surreal short films and directed two features—Tomorrow Night (1998) and Pootie Tang (2001). In 2001, C.K. released his debut comedy album, Live in Houston, directly through his website and became among the first performers to offer direct-to-fan sales of tickets to his stand-up shows and DRM-free video concert downloads via his website. He became prolific releasing nine comedy albums, often directing and editing his specials as well. These specials include Shameless (2007), Chewed Up (2008), Hilarious (2010), and Oh My God (2013).

He gained prominence and widespread acclaim for his FX semi-autobiographical comedy-drama series Louie (2010–2015), which he created, directed and starred in. The series received numerous accolades with C.K. winning two Primetime Emmy Award for Outstanding Writing in a Comedy Series. In 2016, he created and starred in his self-funded web series Horace and Pete, and co-created the shows Baskets and Better Things for FX and voiced the protagonist Max in the animated film The Secret Life of Pets in the same year. During this time he also had supporting acting roles in films such as David O. Russell's American Hustle, Woody Allen's Blue Jasmine (both 2013), and the Hollywood blacklist drama Trumbo (2015).

In 2017, he admitted to several incidents of sexual misconduct following the release of an article in The New York Times. This resulted in widespread criticism and caused his 2017 film I Love You, Daddy to be pulled from distribution prior to its release. In 2018, he returned to stand-up comedy, and in 2019, he announced an international tour. He has also released the specials Sincerely Louis CK (2020) and Sorry (2021) on his website, receiving a Grammy Award for Best Comedy Album for the former. C.K. also co-wrote and directed the film Fourth of July (2022).