Cal Henderson

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Cal Henderson
Cal Henderson in 2010
Callum James Henderson-Begg

17 January 1981 (1981-01-17) (age 43)
Occupation(s)computer programmer, author

Callum James Henderson-Begg (born 17 January 1981), known as Cal Henderson, is a British computer programmer and author based in San Francisco.


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]

Personal life[edit]

Henderson is color blind, and has worked on applications to make the web more accessible to the color 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]


  1. ^ "Cal Henderson is the co-founder of the San Francisco-based Tiny Speck". Sharnbrook Upper School. June 2014.[permanent dead link]
  2. ^ "Slack co-founder Cal Henderson urges graduates to be their own boss". Birmingham City University. Retrieved 1 November 2017.
  3. ^ "Interview with B3ta co-founder Rob Manuel". BBC. August 2005. Retrieved 12 June 2007.
  4. ^ a b Forrest, Conner (13 April 2015). "Cal Henderson: Slack CTO. Author. Science fiction fan". TechRepublic.
  5. ^ a b Honan, Mat. "The Most Fascinating Profile You'll Ever Read About a Guy and His Boring Startup". WIRED. Retrieved 4 May 2018.
  6. ^ "The Team: Web Development Lead: Cal Henderson". Ludicorp. Archived from the original on 11 February 2004.
  7. ^ "O'Reilly catalog - Building Scalable Web Sites". O'Reilly Media. Retrieved 12 June 2007.
  8. ^ "Cal Henderson: Executive Profile & Biography - Bloomberg". Retrieved 4 May 2018.
  9. ^ "City Creator - Yahoo! picks for September 16, 2003". Yahoo!. Archived from the original on 9 January 2007. Retrieved 12 June 2007.
  10. ^ "Stewart Butterfield's Tiny Speck team". 9 February 2010.
  11. ^ "The Next 50 PAC PAC Donors". OpenSecrets. Archived from the original on 27 December 2022. Retrieved 27 December 2022.

External links[edit]