Although not Māori himself, King was well known for his knowledge of Māori culture and history. New Zealand Listener, one of New Zealand's most popular weekly magazines, dubbed King "the people's historian" for his efforts to write about and for the local populace. As a biographer, King published works on Te Puea Herangi, Whina Cooper, Frank Sargeson (1995) and Janet Frame (2000). As an Historian, King's works include Being Pākehā (1985), Moriori (1989), and The Penguin History of New Zealand (July 2003), the latter of which was, by February 2004, into its seventh edition. In all, King wrote, co-wrote and edited more than 30 books on a diverse range of New Zealand topics. He contributed to all five volumes of the Dictionary of New Zealand Biography.