Courier
Designed by Howard Kettler in 1956, Courier was one of the most prevalent fonts of the 1960s, according to Slate, which states that a variation of the font -- Courier New 12, created in 1955 -- was so popular that it is widely considered as "the most recognizable typeface of the 20th century." According to Slate, Kettler was hired by IBM to create typefaces, and Courier quickly became the country's reigning typewriter font due to IBM's dominance in the industry, and because the company failed to trademark the font. As a result, Slate calls Courier an "early version of shareware" since it quickly spread in use by other companies across the country.
Helvetica
Helvetica was invented by freelance designer Max Miedinger in 1957 during his employment at the Haas Type Founder in Switzerland. Miedinger was tasked with redesigning a stripped-down sans serif font called Haas Grotesk. He initially named his recreation Neue Haas Grotesk, but this name was later changed to Helvetica in 1960 when a German company bought the design, and wanted it to have international appeal, according to history website World History Site.
Univers
Adrian Frutiger invented the Univers font in 1956. It was released in 1957 by the Deberny &Peignot type foundry in Paris, and gained popularity as a typewriter font in the 1960s, according to typography resource website Typophile. It is a sans serif font. Typophile states that Frutiger teamed up with Linotype in the 1990s to expand the Univers font family, and there are now over 27 variations of the font.
Letter Gothic
IBM employee Roger Roberson designed the Letter Gothic font between 1956 and 1962, according to the Adobe corporation. Letter Gothic was designed for use in IBM's Selectric typewriters of the 1960s. The typeface was inspired by the Optima font, and originally had flared stems, but transitioned into a monospaced sans serif font, according to Adobe.