Richard Stallman, a key figure in the early hacker community, initiated the free software movement in response to the commercialization of software during the late 1970s and early 1980s. After departing from MIT in 1984, Stallman focused on the GNU project, aiming to create a free Unix-like operating system. In 1985, he established the Free Software Foundation and introduced the GNU General Public License (GPL), a copyleft licensing model that ensures software remains free and open for modification and distribution. Stallman's concept of copyleft, which leverages copyright law to maintain software freedom, became a fundamental principle of the open-source movement. His contributions laid the groundwork for modern free software, impacting significant projects such as GNU Emacs and GCC. Today, the GPL is extensively used by open-source projects like WordPress, GIMP, and Inkscape, underscoring Stallman's lasting influence on the software industry.