Karthik Sivakumar (born 25 May 1977), credited as Karthi, is an Indian actor who works in Tamil Cinema. He is son of veteran actor Sivakumar who began his career as an assistant director in his elder brother Suriya's film Aayutha Ezhuthu (2004). Latter debuted with Paruthiveeran (2007) and recorded a golden debut in Tamil Cinema with six consecutive success. Karthi is an recipient of three Filmfare Awards South and a Tamil Nadu State Film Award.
After a three-year hiatus from acting, he then return to star in films such as Aayirathil Orvuan, Paiyaa and Naan Mahaan Alla, all three of which were released in 2010. He then continued to star in films such as Siruthai (2011), Saguni (2012), Alex Pandian (2013), All In All Azhagu Raja (2013) and Biriyani (2013).
Karthi has starred in several well-known Indian films, portraying an impulsive and short-tempered working-class man in Madras (2014), a paroled convict-turned-caretaker in Tamil-Telugu bilingual comedy-drama film Oopiri / Thozha, and in dual roles as the titular protagonist and the antagonist Raj Nayak in Kaashmora (both in 2016). He also starred as Theeran Thumiran in Theeran Adhigaaram Ondru (2017), for which he was earned for a Filmfare Award South award, as Dilli in Kaithi (2019), as Vallavaraiyan Vandiyadevan in Ponniyin Selvan: I (2022) and its sequel (2023), and in the spy-thriller film Sardar (2022).