Ranganathan Madhavan (born 1 June 1970) is an Indian actor, writer, director, and producer who predominantly appears in Tamil and Hindi films. Over the course of his career, he has been a recipient of several accolades.

Madhavan gained recognition in Tamil cinema by starring in Mani Ratnam's romantic drama film Alai Payuthey (2000). He soon developed an image as a romantic hero with notable roles in two of the highest-grossing Tamil films of 2001, Gautham Vasudev Menon's directorial debut Minnale and Madras Talkies' Dumm Dumm Dumm. He achieved further critical and commercial success with films such as Kannathil Muthamittal (2002), Run (2002), Jay Jay (2003) and Aethirree (2004). In the mid-2000s, Madhavan also actively pursued a career in Hindi films, by appearing in supporting roles in three highly successful productions, Rakeysh Omprakash Mehra's Rang De Basanti (2006), Mani Ratnam's biopic Guru (2007) and Rajkumar Hirani's comedy-drama 3 Idiots (2009), which went on to become the highest-grossing Indian film of all time at the time of its release. During this time, Madhavan also simultaneously continued working in Tamil cinema with the films Evano Oruvan (2007) and Yavarum Nalam (2009).

After appearing in further box office hits, Tanu Weds Manu (2011) and Vettai (2012), Madhavan took a break from acting. Returning after a three-year sabbatical in 2015, his comeback films, the romantic comedy-drama Tanu Weds Manu Returns (2015), the bilingual sports drama Irudhi Suttru (2016) and the crime film Vikram Vedha (2017) all won critical and commercial acclaim. His performance as a boorish boxing coach in Irudhi Suttru fetched him Best Actor awards at the Filmfare, IIFA and SIIMA award ceremonies. Madhavan then worked on his first film as a director with Rocketry: The Nambi Effect (2022), a biopic on Indian rocket scientist Nambi Narayanan, which opened to critical acclaim.

In addition to his acting career, Madhavan has worked as a writer on his films, hosted television programs and has been a prominent celebrity endorser for brands and products. He has also worked as a film producer, first making Evano Oruvan with Leukos Films, before setting up Tricolour Films to produce Saala Khadoos (2016). Madhavan is noted for his philanthropic activities and promotes various causes such as environment, health, and education. He is particularly vocal about the protection of animals and was awarded PETA's Person of the Year recognition in 2011. In 2021, he was conferred the honorary degree of Doctor of Letters by D. Y. Patil Education Society, Kolhapur, for his contribution to arts and cinema.