11 famous people who built their fortunes off their side hustles

These 11 entrepreneurs built their fortunes from ventures that started out as part-time gigs. Not all of them were quick to give up their day jobs, however. Ashton Kutcher has continued to act even after his venture capital firm took off, while Slack's Stewart Butterfield gave the corporate messaging app his full attention after his video game company went under.

DON'T MISS: Meet Masayoshi Son, the billionaire founder of SoftBank and one of the richest men in Japan, who has a $16.3 billion fortune and owns a $117.5 million Silicon Valley estate

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