Short answers, pulled from the story.
The first known use of cryptography dates back to ancient Egypt, where carved ciphertext was discovered on stone. This ancient practice may have been created merely for the amusement of literate observers rather than as a functional tool for concealing information.
Suetonius reports that Julius Caesar used the Caesar cipher to communicate with his generals. This early substitution cipher replaced each letter in the plaintext with a letter three positions further down the alphabet.
The Enigma machine, used by the German government and military from the late 1920s and during World War II, implemented a complex electro-mechanical polyalphabetic cipher. The breaking and reading of the Enigma cipher at Poland's Cipher Bureau for 7 years before the war and subsequent decryption at Bletchley Park was important to Allied victory.
Whitfield Diffie and Martin Hellman proposed the notion of public-key cryptography in a groundbreaking 1976 paper. The race to find a practical public-key encryption system was finally won in 1978 by Ronald Rivest, Adi Shamir, and Len Adleman, whose solution has since become known as the RSA algorithm.
In 1998, U.S. President Bill Clinton signed the Digital Millennium Copyright Act, which criminalized all production, dissemination, and use of certain cryptanalytic techniques and technology. This led to cases like that of Dmitry Sklyarov, who was arrested during a visit to the US from Russia and jailed for five months pending trial for alleged violations of the DMCA.
Estimates suggest that a quantum computer could reduce the effort required to break today's strongest RSA or elliptic-curve keys from millennia to mere seconds. To mitigate this quantum threat, researchers are developing quantum-resistant algorithms whose security rests on problems believed to remain hard for both classical and quantum computers.