Cal Henderson

Henderson attended Sharnbrook Upper School and Community College,^[1] and Birmingham City University where he graduated with a degree in software engineering in 2002.^[2]

Henderson is best known as the co-founder and chief technology officer at Slack, as well as co-owning and developing the online creative community B3ta^[3] with Denise Wilton and Rob Manuel; being the chief software architect for the photo-sharing application Flickr^[4] (originally working for Ludicorp^[5][6] and then Yahoo); and writing the book Building Scalable Web Sites^[7] for O'Reilly Media.

He has also worked for EMAP as their technical director of special web projects^[8] and is responsible for writing City Creator^[9] among many other websites, services and desktop applications. Cal was the co-founder and VP of engineering at Tiny Speck,^[10] the company whose internal tool transitioned into Slack.

Henderson's connection to Stewart Butterfield and Slack began through a game developed by Butterfield's first company, Ludicorp, called Game Neverending. He ran a fan website dedicated to the game and broke into an internal Ludicorp mailing list. Instead of repercussions, Butterfield hired Henderson to work for his company.^[5]

Henderson is colour blind, and has worked on applications to make the web more accessible to the colour blind.^[4] He is also a frequent contributor to open-source software projects and runs a number of utility websites, such as Unicodey, to make certain programming tasks easier.

In August 2022, Henderson contributed $50,000 to The Next 50, a liberal political action committee (PAC).^[11]