TCP/IP is a communications protocol suite that underpins the Internet. TCP/IP refers to the two core protocols of the suite:
The modern Internet is named after the Internet Protocol (IP): the Internet Protocol (IP) enables computer networks to easily interconnect, becoming interconnected networks.
TCP/IP was designed in the 1970's and it's development was funded by the U.S. Department of Defense. DARPA, an agency of the U.S. Department of Defense, was the agency that directly funded and controlled the development of TCP/IP. DARPA stands for 'Defense Advanced Research Projects Agency' and funds technology for the United States military. DARPA was created in 1958 by the U.S. President Dwight David "Ike" Eisenhower; who had previously been Supreme Commander of the Allied Forces in Europe during World War 2.
Development of TCP/IP began in 1973, and it's designers were Bob Kahn and Vint Cerf. In 1975, DARPA contracted three research/academic institutions to develop a working version of the protocol. In 1982, the U.S. Department of Defense declared that TCP/IP would become a 'standard' for all their military computer networks. TCP/IP was referred to as DoD TCP/IP, because the protocol suite was funded and owned by the U.S. Department of Defense.
Due to the success of TCP/IP, it was implemented on a range of federally funded U.S. computer networks: like NSFNET and ARPANET. During the 1980's, these networks voluntarily agreed to interconnect - using TCP/IP - and this 'network of networks' was referred to as the Internet.
The U.S. federal government decided to stop funding the development of TCP/IP in the early 1990's, and leadership of it's development was handed to the Internet Society. The Internet Society is an international non-profit organisation. Therefore, TCP/IP was no longer referred to as DOD TCP/IP, but simple: TCP/IP. Eventually, TCP/IP would be named as the Internet protocol suite.