Courier is a monospaced slab serif “typewriter” font designed by Howard Kettler in 1955. Adrian Frutiger later redrew Courier for use in the IBM Selectric series of electric typewriters. IBM chose not to seek any kind of copyright protection for Courier so the typeface is now available for royalty-free use. This has made it a common “web safe” font. I like Courier, however I think there are other monospaced fonts that offer better legibility on screen, such as Anonymous Pro.
Font research done for you.