William Yeager is an American engineer who is best known for being the inventor of a packet-switched, "Ships in the Night," multiple-protocol router in 1981, during his 20-year tenure at Stanford's Knowledge Systems Laboratory. The code was licensed by upstart Cisco Systems in 1987 and comprised the core of the first Cisco IOS. He is also known for his role in the creation of the IMAP mail protocol, and for writing the ttyftp serial line file transfer program, which was developed into the MacIntosh version of the Kermit protocol at Columbia University. He has also worked 5 years for NASA Ames Research Center and 10 years at Sun Microsystems. At Sun as the CTO of Project JXTA.