Ishak Haji Muhammad (14 November 1909 – 7 November 1991), better known as Pak Sako, was a Malaysian writer, active in the 1930s until the 1950s. He was a nationalist and his involvement began before independence and continued thereafter. He fought for the idea of the unification of Melayu Raya where Indonesia, Malaysia and Brunei are united in one collective.
The moniker Pak Sako was from the title 'Isako-san' given to him by the Japanese, which was the phonetic pronunciation of his name in the Japanese tongue. Ishak's other pseudonyms include Anwar, Hantu Raya (The Great Ghost), Isako San and Pandir Moden (The Modern-day Pandir).