Peter Thomas Kirstein CBE FREng DFBCS FIET FInstP (20 June 1933 – 8 January 2020) was a British computer scientist who played a role in the creation of the Internet. He put the first computer on the ARPANET outside of the US and was instrumental in defining and implementing TCP/IP alongside Vint Cerf and Bob Kahn. Kirstein is "often recognized as the father of the European Internet".