Ray Tomlinson, one of the early ARPAnet pioneers in the 1960s at engineering firm Bolt Beranek and Newman (BBN), died Saturday morning of a suspected heart attack. He was 74.

Tomlinson was best known for choosing the @ symbol to indicate a message should be sent to a different computer on a network. He also led development of standards for the from, subject, and date fields found in every email message sent today.

He earned a bachelor of science in electrical engineering from Rensselaer Polytechnic Institute in 1963 and a master’s in electrical engineering from the Massachusetts Institute of Technology in 1965, where he worked on speech synthesis.

News of his death began circulating on a BBN alumni email list tonight. Another networking legend, TCP/IP inventor Vint Cerf, confirmed it via Twitter.

Tomlinson was inducted into the Internet Hall of Fame in 2012. Memories from fellow BBN employees are documented here (PDF).

Tomlinson’s death is the third passing of an MIT-educated computer industry legend this year. Artificial intelligence expert Marvin Minsky died in January, and personal computing innovator Wesley A. Clark died in February. Both were 88.