Singanalluru Puttaswamaiah Muthuraj (24 April 1929 – 12 April 2006), better known by his stage name Dr. Rajkumar, was an Indian actor, singer and producer who worked in Kannada cinema. Through his over five-decade long career of over 200 films, he was regarded one of the most pivotal and influential figures of the Kannada film industry. His films were praised for acting as a bridge between the popular and art films because of the theme of the story and their treatment. He debuted as a child actor in the 1942 Kannada film Bhakta Prahlada. His first role as an adult came in Sri Srinivasa Kalyana (1952) and as a lead, two years later, in Bedara Kannappa, which gave him stardom. He debuted as a singer with the track Om Namaha Shivaya from the 1956 film Ohileshwara. In 1960, he made his debut as a producer by producing Ranadheera Kanteerava. According to Ashish Rajadhyaksha and Paul Willemen in the book Encyclopedia of Indian Cinema, Ranadheera Kanteerava was the first "big hit" in Kannada cinema. In a film career spanning fifty years, Rajkumar received eleven Karnataka State Film Awards, including nine Best Actor and two Best Singer awards, eight Filmfare Awards South, and one National Film Award. Along with Vishnuvardhan and Ambareesh, he is counted in Kannada cinema's "triumvirate" as its most celebrated actor.

In 1983, Rajkumar was honoured with the Padma Bhushan, India's third highest civilian award, for his contributions to Indian cinema, and the Dadasaheb Phalke Award in 1995. In 1985, he became the first Indian actor to receive the Kentucky Colonel, an honorary order from the governor of Kentucky, United States. On the occasion of the "Centenary of Indian Cinema" in April 2013, Forbes included his performance in Bangaarada Manushya on its list of "25 Greatest Acting Performances of Indian Cinema". Upon his death, The New York Times had described him as one of India's most popular movie stars. He received the NTR National Award in 2002 and was awarded an honorary doctorate from the University of Mysore. Dr. Rajkumar Samagra Charithre - a two-volume book by film critic D. Rukkoji on the life and achievements of Rajkumar won the Swarna Kamal Award at the 63rd National Film Awards under the National Film Award for Best Book on Cinema category. On the occasion of Rajkumar's 100th film Government of Karnataka honored him with the title of Nata Saarvabhouma. He is also the first film star to win the National Film Award for Best Male Playback Singer for the song Naadamaya Ee Lokavella from the film Jeevana Chaitra. The State Government established Dr. Rajkumar Award in 1993–94 to be given for lifetime achievement towards contributions to Kannada cinema.

Dr. Rajkumar's 1972 film Bangaarada Manushya was the longest running South Indian film at the time of its release. The film elevated him from being just another very popular actor to nearly demigod status among the masses. His 1986 film Anuraga Aralithu was the first Indian film to be remade in seven other languages. His 1973 film Gandhada Gudi was reported to be the first Indian film to be made on the concept of protection of forest and wildlife conservation with a focus on the need to preserve the flora and fauna at a time when the CITES treaty was signed with an aim to reduce the economic incentive to poach endangered species. The British daily newspaper The Guardian praised him for his subtle acting and described him as a humble, modest being who was a symbol of Kannada consciousness. ABC News acknowledged him as one of the greatest actors of his time and called him The Gentle Giant of Karnataka. In 2016, the Maharashtra State Government had prescribed the biography of the actor for its class VIII students detailing his achievements and contributions to the Kannada culture under the title Natasarvabhouma. In 1989, the critical failure of Parashuram led him to take a hiatus from acting. However, he returned to acting three years later, in 1992 with Jeevana Chaitra, which was a blockbuster running for more than a year in theatres. His final film was 2000's Shabdavedhi. He had a minimum of ten releases in each of the years from 1963 to 1971. He held the record for highest releases as a lead in a single year (16 in 1968) in Kannada movies for 24 years until it was broken by Malashri in 1992 with 19 releases.