Stewart Butterfield

Flickr supplied experience before the company that created most of the fortune

Butterfield was chief executive of Ludicorp, the company that developed Flickr, before Yahoo acquired the business in 2005. Slack's later securities filing records that he stayed at Yahoo as Flickr's general manager until 2008, giving him an earlier founder exit and operating experience before Slack. ^[1]

The company that became Slack was incorporated in 2009 as Tiny Speck. It initially pursued a browser game, but the team had built an internal messaging system for its own work; Forbes reported that this communication tool became the product around which Butterfield and his cofounders rebuilt the company. ^[1][2]

Slack launched as a workplace software service and attracted substantial venture backing as adoption grew. Butterfield remained cofounder, chief executive and board chairman, so the company's growth translated into a large founder equity position rather than only executive compensation. ^[1][2]

The direct listing put a market price on founder ownership

Slack entered the public market through a direct listing in June 2019 instead of issuing new shares in a conventional IPO. Forbes estimated Butterfield owned about 7% at the debut, and the opening share price valued that stake at roughly $1.6 billion. ^[2]

That listing clarifies the mechanism behind Butterfield's wealth: venture financing diluted ownership as Slack scaled, but he retained enough founder equity for the public market to make the stake billionaire-scale. Slack's full company valuation therefore was not his fortune; his attributable stake was the relevant asset. ^[2][1]