Datu Mustapha bin Datu Harun, or Tun Mustapha for short (31 July 1918 – 2 January 1995[2][3]), was a Malaysian politician who served as the 3rd Chief Minister of Sabah from May 1967 to November 1975 and the 1st Yang Di-Pertua Negara from September 1963 to September 1965 and President of the United Sabah National Organisation (USNO).

The revolt failed and the Japanese engaged in large scale massacres of indigenous civilians, including women and children especially from the Suluks community.

In the end, a compromise was reached when Mustapha obtained increased USNO representations in Sabah government's cabinet while Stephens retained his chief minister post.

Although the central government, represented by the Barisan Nasional (BN) coalition, was a partner of USNO, they were worried about certain stances taken by Mustapha, in particular, his intention or threat to secede Sabah from Malaysia.

Since his ouster in 1976, Tun Mustapha had been trying to initiate a merger of his party USNO with peninsular-based United Malays National Organisation (UMNO) in a bid to return to the corridors of power in Sabah.

[citation needed] Mustapha remained active in politics, leading USNO and contesting in four subsequent state elections (1981, 1985, 1986, and 1990).

[citation needed] Mustapha is remembered negatively by the Catholics (what more other Christians in general) of Sabah for imposing to the letter the immigration laws by denying foreign priests as well as missionary pastors who have not obtained permanent residency on the extension of their visas.

All the priests who object to their expulsion for doing religious proselytization among the Catholics and also other Christians were eventually arrested by using his powers as Chairman of the State Security Operation Committee in his capacity as the Chief Minister of Sabah.

[11] Under his orders, on 2 December 1972, the police made a raid at the missions at Bundu Tuhan (Ranau), Papar, Tambunan and Kuala Penyu.

The raids at Tambunan and Papar were successful, timed early in the morning with the church bell ropes cut to prevent it from being used to warn the people.

[12] The rest of the priests who only had temporary residence permits, on hearing this has no choice but to say goodbye to their parishioners and went home or were given new assignments to nearby countries.

The reason was that the book "allegedly" recorded that Mojuntin exposed Mustapha's attempt to stop Catholicism in Sabah by deporting and arresting foreign missionary priests who were serving their local parishes in the state.

[15] He actively sponsored the creation of United Sabah Islamic Association (USIA) on 14 August 1969 which was modelled from similar agencies that already existed in West Malaysia.

He was then later buried at the Muslim cemetery in Kampung Ulu/Ulu Seberang, Putatan, Penampang (prior to that, his mortal remains were laid in state at his residence in the Tanjung Aru suburb of Kota Kinabalu city after it arrived home from the Sabah Medical Centre hospital in Likas, which is now today rebranded as a public government hospital known as the Sabah Women's and Children Hospital) which was formerly used as a fortress by the late Paduka Mat Salleh and the State Government has named the cemetery "Taman Memorial Tun Datu Haji Mustapha."

During the 8th Convocation Ceremony of UMS (Universiti Malaysia Sabah) held on 2–3 September 2006, he was conferred a Doctor of Philosophy in (Social Development) posthumously.