Short answers, pulled from the story.
President Sukarno banned the Masyumi Party in 1960 after three of its senior leaders, Mohammad Natsir, Sjafruddin Prawiranegara, and Burhanuddin Harahap, joined the PRRI rebellion in Padang, Sumatra, and the party refused to condemn their actions. Sukarno passed a law allowing him to ban parties whose members had rebelled against the state, then applied it directly to Masyumi.
The Masyumi Party traces its origins to a trade organization called the Islamic Trading Association, founded in Java in 1909 to protect batik traders from competition. After evolving through several name changes, the post-independence Masyumi was formed on the 17th of August 1945 as an umbrella party for Muslim organizations, deliberately adopting the name of a Japanese-era council in order to use its nationwide network.
Masyumi won 7,903,886 votes in the 1955 parliamentary election, representing 20.9 percent of the popular vote and 57 seats in the legislature. The party came in second place and was the dominant party in regions outside Java, leading among roughly one third of Indonesians living beyond the island.
The main leaders of the Masyumi Party were Mohammad Natsir, Mohammad Roem, Sjafruddin Prawiranegara, Jusuf Wibisono, and Abu Hanafi. Natsir was the most prominent figure, leading one of the party's two main internal factions and serving as Prime Minister after Sukarno asked him to form a cabinet in 1950.
Nahdlatul Ulama voted at its 1952 congress to become an independent political party, following a prolonged dispute that included the Masyumi-backed cabinet's refusal to reappoint the prominent NU figure Wahid Hasyim as religious affairs minister. The departure stripped Masyumi of its claim to represent all Indonesian Muslims.
After the ban, former members formed the Crescent Star Family to continue campaigning for Islamic law. In 1967, Natsir and Mohammad Roem established the Indonesian Islamic Propagation Council, operating from the old Masyumi headquarters. The government later permitted a successor party, Parmusi, in 1968, but barred former Masyumi members from leading it.