Margaret Hamilton, who led software engineering for NASA's Apollo program, died at age 90. Her work on the Apollo Guidance Computer helped navigate spacecraft to the moon and enabled the first human landing in 1969. Hamilton directed the team at MIT's Instrumentation Laboratory that developed the computer's software, including the display and keyboard interface known as DSKY. The AGC, one of the first computers using silicon integrated circuits, controlled both the command module in lunar orbit and the lunar module that descended to the surface. During Apollo 11's descent, alarms sounded due to an inadvertently activated radar switch. Hamilton's prior simulations and guidance to mission controllers allowed the landing to continue, a moment she later called the most exciting of her life. Born in Indiana in 1934, Hamilton studied mathematics before joining MIT's meteorology department. She later became the first programmer for Apollo and the first woman in the project's leadership role. Her team wove core memory by hand, a process she helped formalize as 'software engineering.' After Apollo, she worked on Skylab and the space shuttle, founded two software companies, and received numerous honors including the Presidential Medal of Freedom in 2016. Her daughter survives her; her other marriages ended in divorce.