BARISAN NASIONAL (BN)
13-party ruling coalition led by Umno.
Datuk Seri Najib Razak, 64
Posts: Prime Minister of Malaysia; Finance Minister; Umno president; chairman of BN; MP for Pekan (Pahang)
His political career began in 1976, when he was just 23 years old. He ran for and won the parliamentary seat in Pekan, Pahang, left vacant by his father's death. His father Tun Abdul Razak Hussein was Malaysia's second prime minister.
Datuk Seri Najib became Malaysia's youngest menteri besar in 1982, for Pahang, a record that still stands. He was 29. He took over as president of Umno from Tun Abdullah Badawi in March 2009. Mr Najib had held various Cabinet positions before taking over as the country's sixth Prime Minister in April 2009.
Umno has 86 seats in Parliament, the most among the 13 Barisan Nasional parties. These 86 wards form nearly 40 per cent of the 222-member Parliament, allowing Mr Najib to secure control of Malaysia as long as he has the party's loyalty. The party is now behind him after he expelled, in 2016, then-deputy president Muhyiddin Yassin, who had called for Mr Najib's resignation amid graft allegations surrounding state fund 1Malaysia Development Bhd (1MDB).
PAKATAN HARAPAN (PH)
Four-party opposition alliance.
Tun Mahathir Mohamad, 92
Posts: Chairman of opposition party PPBM; chairman of opposition alliance PH
Dr Mahathir was Malaysia's prime minister between 1981 and 2003. During his 22-year rule, the no-nonsense leader brought rapid modernisation and economic growth but also weakened independent institutions, from the judiciary to graft-busters.
He remains a vocal critic of the government after retiring in October 2003. Dr Mahathir quit Umno in May 2008 after a falling out with then-Prime Minister Abdullah Badawi. The elderly politician rejoined Umno in April 2009 soon after Datuk Seri Najib Razak became the country's Prime Minister. But in February 2016, Dr Mahathir again left Umno, this time over the 1MDB scandal.
In September 2016, Dr Mahathir formed a new political group, Parti Pribumi Bersatu Malaysia (United Indigenous Party of Malaysia, PPBM), with former deputy prime minister Muhyiddin Yassin, and his son former Kedah menteri besar Mukhriz Mahathir. He later found support from his former political foes in the opposition to lead the four-party opposition alliance Pakatan Harapan (PH).
PARTI ISLAM SEMALAYSIA (PAS)
Abdul Hadi Awang, 70
Posts: President of PAS; MP for Marang (Terengganu); state assemblyman Rhu Rendang (Terengganu)
The ultra-conservative Tuan Guru (master teacher) leads some one million members who make up Malaysia's second-largest political party by membership, Parti Islam SeMalaysia (PAS).
He consolidated his power base in 2015 after revered PAS spiritual leader Nik Aziz Nik Mat died and the more liberal leaders left the party after fractious internal polls. A fiery speaker, Datuk Seri Hadi pulled PAS out of the opposition alliance, introduced a stronger Islamist outlook and brought the party closer to ruling party Umno.