Many people know about Alex from his software, his responsibilities at Automattic on the Jetpack team, and his long-time involvement in the WordPress community.
Stephane Daury offered a better picture of Alex's life than I ever could.
Matt Mullenweg shared some pictures of Alex over the years.
Alex's popular Regenerate Thumbnails WordPress plugin recently passed 10 million downloads, with over one million active installs.
There's no doubt that Alex's influence and work will live on for a long time to come. Rest in peace, Alex.