Ajith Kumar Subramaniam (born 1 May 1971) is an Indian actor who works predominantly in Tamil cinema. To date, he has starred in over 63 films, and won four Vijay Awards, three Cinema Express Awards, three Filmfare Awards South and three Tamil Nadu State Film Awards. In addition to his acting career, Ajith is an occasional racing driver and participated in the MRF Racing series (2010) and having competed in circuits around India in places such as Mumbai, Chennai and Delhi. He is one among very few Indians to race in the international arena and in Formula championships. Based on the annual earnings of Indian celebrities, he was included in the Forbes India Celebrity 100 list three times.

Ajith began his career with a small role in the 1990 Tamil romantic drama En Veedu En Kanavar. After his success in Rajavin Parvaiyile, his first major breakthrough was Aasai (1995), Ajith established himself as a romantic hero with Kadhal Kottai (1996), Kaadhal Mannan (1998) and Aval Varuvala (1998), and established himself as an action hero starting with the film Amarkkalam (1999). Ajith's dual portrayal of twin brothers—where one is deaf-mute—in S. J. Suryah's Vaalee (1999) won him his first Filmfare Award for Best Actor – Tamil. He earned critical acclaim for his dual roles in the vigilante film Citizen (2001). He was also praised for his dual role performance in K. S. Ravikumar’s Villain (2002) where he won his second Filmfare Award for Best Actor - Tamil. In 2006, he starred in K. S. Ravikumar's Varalaru, in which he played three roles including one of a classical Bharatanatyam dancer. It became the highest-grossing Tamil film of 2006, and earned him another Filmfare Award for Best Actor – Tamil. The following year he starred in two remakes—Kireedam (2007) and Billa (2007), both of which earned him critical acclaim. Ajith played an antagonist in his 50th film Mankatha (2011), which became one of the highest-grossing Tamil films of all time. His next release, Billa II (2012), was Tamil cinema's first prequel.

Ajith has also been abroad for various races, including Germany and Malaysia. He drove in the 2003 Formula Asia BMW Championships. He raced in the 2010 Formula 2 Championship along with two Indians, Armaan Ebrahim and Parthiva Sureshwaren. In 2025, Government of India honoured him with Padma Bhushan, the nation's third highest civilian honour.

Ajith Kumar was born on 1 May 1971 in Secunderabad, present-day Telangana, India. His father, P. Subramaniam (died 2023), was from a Tamil Palakkad Iyer family from Kerala and his mother, Mohini, is a Sindhi from Kolkata, West Bengal. Ajith was the middle son out of three brothers, one of his other brothers is Anil Kumar, an IIT Madras graduate-turned-entrepreneur, and the other one is Anup Kumar.

Ajith dropped out of Asan Memorial Senior Secondary School during his tenth grade, before he had completed his higher secondary schooling. Through a family friend who worked with the Enfield company, Ajith was able to get a job as an apprentice and spent six months training to be a mechanic. He later quit the role at the insistence of his father, who wanted Ajith to have a white-collar job, and joined another family friend's garment exporting company as an apprentice. He eventually progressed to become a business developer and regularly travelled throughout the country on sales assignments, improving his English-speaking skills. After resigning from the role, Ajith set up a textiles business distributing fabric alongside three other partners. The business venture underperformed prompting Ajith to take up another job in the garments industry. During the period, Ajith also began working on modelling assignments alongside his work. He was notably scouted by P. C. Sreeram during the making of a commercial for Hercules Cycle and Motor Company, who felt he had the appearance to become an actor.

Ajith began his acting career through a one-scene appearance as a school child in En Veedu En Kanavar (1990). Through the recommendation of S. P. Balasubrahmanyam, whose son, S. P. Charan, was a classmate of his, he was cast in his first lead role in the Telugu romantic drama Prema Pusthakam (1993), which remains his only Telugu film to date. However, the shoot of the film was stalled soon after production began, following the death of the film's director, Gollapudi Srinivas. As a result, his first major theatrical release was the Tamil romantic drama Amaravathi (1993), which Ajith had signed after being recommended to director Selva by Balasubrahmanyam, who had seen parts of Prema Pusthakam prior to its delay. As the film went into post-production, Ajith was bed-ridden due to a racing injury while training for an amateur motor race. He underwent three major surgeries resulting in bed rest for one and a half years. As a result, his voice in the film was dubbed by actor Vikram. Following the injury, Ajith was keen to make up for lost time and signed on to play supporting roles. In the following years, he played character roles in the Arvind Swami-starrer Paasamalargal (1994) and Vijay-starrer Rajavin Parvaiyile (1995). He was also seen in the family drama Pavithra (1994), which featured him as an ailing patient shown maternal affection by Radhika's character.

Ajith's first commercially successful film as a lead actor was the romantic thriller Aasai (1995). The film, directed by Vasanth and produced by Mani Ratnam featured him in the lead role opposite Suvalakshmi, whose brother-in-law lusts for her. It performed well at the box office and established Ajith as an upcoming actor in the Tamil film industry. Aasai also earned him his first nomination for the Filmfare Award for Best Actor – Tamil. He later played a college student in Kalloori Vaasal, co-starring Prashanth and Pooja Bhatt. Ajith's second successful film came in the form of National Award winning Kadhal Kottai, in which Ajith reunited with Agathiyan, the director of the earlier project Vaanmathi. The film paired him opposite Devayani, with Heera Rajgopal playing a supporting role.

In 1997, Ajith appeared in five consecutive failures. During the same period, he had entered into the film distribution business and had experienced losses as a result. Describing the period as a "cruel time", Ajith also continued to have chronic back injuries and several of his other film commitments had become delayed. A notable project among the five films was Amitabh Bachchan's Tamil production Ullaasam (1997), in which he was paid a high salary of ₹2 million (equivalent to ₹11 million or US$130,000 in 2023) for the first time.