Question: Which of the people with which S. K. Sikka played a crucial role was an Indian physicist who is best known for his role in India's nuclear program during its early stages?

Context paragraphs:
Igor Kurchatov: Igor Vasilyevich Kurchatov (Russian: И́горь Васи́льевич Курча́тов ; 8(21) January 1903 – 7 February 1960), was a Soviet nuclear physicist who is widely known as the director of the Soviet atomic bomb project.  Along with Georgy Flyorov and Andrei Sakharov, Kurchatov is widely remembered and dubbed as the "father of the Soviet atomic bomb" and later, "the father of the Soviet Nuclear Missile" for his directorial role in the development of the Soviet nuclear program, in a clandestine program during World War II formed in the wake of the USSR's discovery of the Western Allied efforts to develop nuclear weapons.  After nine years of covert development, the Soviet Union successfully tested its first nuclear weapon, codenamed "First Lightning" at the Semipalatinsk Test Range in 1949.  In 1954 he was awarded the USSR State Prize in physics.

S. K. Sikka: Satinder Kumar Sikka is an Indian nuclear condensed matter physicist, crystallographer and a former Scientific Secretary to the Principal Scientific Advisor of the Government of India.  He is known to have played a crucial role, along with Raja Ramanna, Rajagopala Chidambaram and Basanti Dulal Nagchaudhuri, in the design and development of a Hydrogen Bomb by India, which was tested at the Pokhran Test Range in May 1998, under the code name, Operation Shakthi.  He was also involved in the Smiling Buddha tests, conducted in 1974.  He was awarded the fourth highest civilian award of the Padma Shri, by the Government of India, in 1999.

India–United States Civil Nuclear Agreement: The 123 Agreement signed between the United States of America and the Republic of India is known as the U.S.–India Civil Nuclear Agreement or Indo-US nuclear deal.  The framework for this agreement was a July 18, 2005, joint statement by then Indian Prime Minister Manmohan Singh and then U.S. President George W. Bush, under which India agreed to separate its civil and military nuclear facilities and to place all its civil nuclear facilities under International Atomic Energy Agency (IAEA) safeguards and, in exchange, the United States agreed to work toward "full" civil nuclear cooperation with India.  This U.S.-India deal took more than three years to come to fruition as it had to go through several complex stages, including amendment of U.S. domestic law, especially the Atomic Energy Act of 1954, a civil-military nuclear "Separation Plan" in India, an India-IAEA safeguards (inspections) agreement and the grant of an exemption for India by the Nuclear Suppliers Group, an export-control cartel that had been formed mainly in response to India's first nuclear test in 1974.  In its final shape, the deal places under permanent safeguards those nuclear facilities that India has identified as "civil" and permits broad civil nuclear cooperation, while excluding the transfer of "sensitive" equipment and technologies, including civil enrichment and reprocessing items even under IAEA safeguards.  On August 18, 2008 the IAEA Board of Governors approved, and on February 2, 2009, India signed an India-specific safeguards agreement with the IAEA.  After India brought this agreement into force, inspections began in a phased manner on the 35 civilian nuclear installations India has identified in its Separation Plan. <ref name="INFCIRC/731"> </ref> The deal is seen as a watershed in U.S.-India relations and introduces a new aspect to international nonproliferation efforts.  On August 1, 2008, the IAEA approved the safeguards agreement with India, after which the United States approached the Nuclear Suppliers Group] (NSG) to grant a waiver to India to commence civilian nuclear trade.  The 48-nation NSG granted the waiver to India on September 6, 2008 allowing it to access civilian nuclear technology and fuel from other countries.  The implementation of this waiver made India the only known country with nuclear weapons which is not a party to the Non-Proliferation Treaty (NPT) but is still allowed to carry out nuclear commerce with the rest of the world.

Waman Dattatreya Patwardhan: Waman Dattatreya Patwardhan (January 30, 1917 - July 27, 2007) was an Indian nuclear chemist, defence scientist and an expert in the science of Explosives engineering.  He was the founder director of the Explosives Research and Development Laboratory (now known as the High Energy Materials Research Laboratory (HEMRL)) of India.  He is considered one of the distinguished scientists in India due to his contributions to Indian space program, Indian nuclear program and missile program in their early stages.  He developed the solid propellant for India's first space rocket launched at Thumba.  He was responsible for developing the detonation system of India's first nuclear device which was successfully tested in 1974, an operation codenamed Smiling Buddha.

K. Sankaran Nair: K. Sankaran Nair (1919–2015), known as Colonel Menon among his colleagues, was an Indian civil servant, diplomat and the director of Research and Analysis Wing (RAW), the apex intelligence agency in India.  He served as the Indian High Commissioner to Singapore from 1986 to 1988 and was the last member of the Indian Imperial Police.  He was reported to have played a crucial role in the formation of Bangladesh, through RAW operations during the Bangladesh Liberation War.  His memoirs, "Inside IB and RAW: A Rolling Stone that Gathered Moss", published in 2008 made news for the insider details it contained about two of the highest intelligence agencies in India.  The Government of India awarded him the third highest civilian honour of the Padma Bhushan, in 1983, for his contributions to society.

Homi Sethna: Homi Nusserwanji Sethna PhD (24 August 1923 – 5 September 2010) was an Indian nuclear scientist and a chemical engineer, gaining international fame as the Chairman of the Atomic Energy Commission (India) during the time when the first nuclear test, codename "Smiling Buddha" in Pokhran Test Range in 1974 was conducted.  He was the primary and central figure in India's civilian nuclear program as well as the construction of nuclear power plants.

P. K. Iyengar: Padmanabha Krishnagopala Iyengar (29 June 1931 – 21 December 2011; best known as P. K. Iyenger), was an Indian nuclear physicist who is widely known for his central role in the development of the nuclear program of India.  Iyengar previously served as the director of BARC and former chairman of the Atomic Energy Commission of India, he raised his voice and opposition against the nuclear agreement between India and the United States and expressed that the deal favoured the United States.

Kurt Diebner: Kurt Diebner (13 May 1905 – 13 July 1964) was a German nuclear physicist who is well known for directing and administrating the German nuclear energy project, a secretive program aiming to build nuclear weapons for Nazi Germany during the course of World War II.  Diebner was the administrative director of the German nuclear program after Adolf Hitler, Führer and Reich Chancellor, authorized this program.

Jafar Dhia Jafar: Jafar Dhia Jafar (Arabic: جعفر ضياء جعفر‎ ‎ ; born: 1943) is an Iraqi nuclear physicist, former Vice Chairman of the Iraq Atomic Energy Commission, and chief of Iraq's nuclear program.  He is widely known as the father of the Iraqi Nuclear Program.

Raja Ramanna: Raja Ramanna "ರಾಜಾ ರಾಮಣ್ಣ" (Kannada) (28 January 1928 – 24 September 2004) was an Indian physicist who is best known for his role in India's nuclear program during its early stages.

Supporting paragraphs: S. K. Sikka Raja Ramanna
Answer: Raja Ramanna