Mahathir bin Mohamad (Jawi: محاضير بن محمد; IPA: [mahaðɪ(r) bɪn mohamad]; born 10 July 1925) is a Malaysian politician, author, and physician who served as the 4th and 7th Prime Minister of Malaysia. He held the office from July 1981 to October 2003 and later from May 2018 to March 2020 for a cumulative total of 24 years, making him the country's longest-serving prime minister, as well as the first and only person to be appointed Prime Minister twice. Before becoming premier, he served as Deputy Prime Minister and in other cabinet positions. He was a Member of Parliament for Langkawi from May 2018 to October 2022, Kubang Pasu from August 1974 to March 2004, and Kota Setar Selatan from April 1964 to May 1969. His political career has spanned more than 75 years, from joining protests opposing citizenship policies for non-Malays in the Malayan Union in the 1940s to forming the Gerakan Tanah Air coalition in 2022.

Born and raised in Alor Setar, Kedah, Mahathir excelled at school and became a physician. He became active in the United Malays National Organisation (UMNO) before entering the Parliament of Malaysia in 1964. He served one term before losing his seat, subsequently falling out with Prime Minister Tunku Abdul Rahman and being expelled from UMNO. He wrote The Malay Dilemma during this period, which formed the basis of future ethnic Malay affirmative action policies in the country. When Abdul Rahman resigned, Mahathir re-entered UMNO and parliament, and was promoted to Minister of Education from 1974 to 1978 and Minister of Trade and Industry from 1978 to 1981. He became Deputy Prime Minister in 1976. In 1981, he was sworn in as prime minister following the resignation of Hussein Onn.

During Mahathir's first tenure as prime minister, Malaysia experienced a period of rapid modernization and economic growth, and his government initiated widespread industry privatisation and a series of bold infrastructure projects. Mahathir was a dominant political figure, winning five consecutive general elections and fending off a series of rivals for UMNO's leadership. However, his power accumulation came at the expense of judicial independence and the Malaysian royalty's traditional powers and privileges. He continued pro-bumiputera affirmative action policies, but in the 1990s introduced the Bangsa Malaysia policy that saw some political liberalisation. He used the controversial Internal Security Act to detain activists, non-mainstream religious figures, and political opponents in 1987 Operation Lalang and later his own Deputy Prime Minister Anwar Ibrahim, whom he fired in 1998. Mahathir's record of curtailing civil liberties in Malaysia as well as his antagonism towards Western interests and economic policy made his relationships with Western nations difficult. As prime minister, he was an advocate of Asian development models and values, and was prominent across the Muslim world.

After retiring in 2003, Mahathir became a strident critic of his hand-picked successor Abdullah Ahmad Badawi, and later Najib Razak. In 2016, Mahathir quit UMNO over the 1MDB corruption scandal. As part of the Malaysian United Indigenous Party (BERSATU), he went on to lead the Pakatan Harapan opposition to victory in the 2018 general election. Mahathir became the first Malaysian prime minister not to represent the Barisan Nasional (BN) coalition (or its predecessor, the Alliance Party), and the first to serve non-consecutive terms. In his second tenure, Mahathir prioritised reopening investigations into the 1MDB scandal, combatting corruption and "restoring the rule of law", and cutting spending on large infrastructure projects such as those under the Belt and Road Initiative. Prior to the election, Mahathir promised to seek a pardon for Anwar Ibrahim and hand over the premiership to him after an unspecified interim period.

In 2020, Mahathir's refusal to commit to handing over the office of Prime Minister to Anwar contributed to a political crisis that led to Mahathir's resignation as Prime Minister and the collapse of the Pakatan Harapan government. At the time of his resignation, he was the world's oldest serving state leader at the age of 94. Mahathir left BERSATU in protest of its new coalition with UMNO and formed the Homeland Fighters Party and coalition Gerakan Tanah Air. Mahathir subsequently lost his parliamentary seat for Langkawi and his election deposit in the 2022 general election.