Skip to Content
  • Age
  • Title
    CTO and cofounder
  • Company

Industry: Tech

Cal Henderson has a talent: building wildly valuable “dumb side projects” out of his true passion, gaming companies. In 2002, Henderson was so fascinated by an online gaming startup known as Ludicorp that he helped now Slack CEO Stewart Butterfield build image-sharing platform Flickr to keep the lights on. While the Ludicorp game that inspired Flickr didn’t work out, Flickr sold to Yahoo for $35 million. Fast-forward to 2014: Henderson and Butterfield programmed yet another game that failed to take off but had given birth to a successful internal messaging system. That system became Slack, the wildly popular workplace communication tool that makes users feel as if they are part of something more than the daily grind. Slack now has 1,500 employees and over 10 million active users, and it just went public via a well-received direct listing on the NYSE. One major innovation Slack users can trace back to Henderson: Slack’s thousands of emojis. Will he deliver a third transformative product? Perhaps. Henderson is still an active member of Slack’s internal “Games We Won’t Finish” chat channel.


40 Under 40

List Debut