Which dragon co-founded Social Chain before joining the British programme Dragons' Den?

Steven Bartlett co-founded Social Chain before joining the British programme Dragons' Den.

Steven Bartlett is a British entrepreneur, author and podcaster who co-founded Social Chain, a social-media marketing agency. His career was built in digital media and online communities, giving him a background different from dragons whose businesses were established in retail, property or manufacturing.

Bartlett joined the British panel as a comparatively young technology and media-focused investor. His presence broadened the range of experience represented in the den, particularly for companies whose customers and marketing depend on social platforms.

Social Chain is sometimes confused with Bartlett’s later media activities, including podcasting and writing. Those are separate parts of his career. The precise fact asked here is the company he co-founded before his Dragons' Den role: Social Chain, not his podcast or a business pitched by another contestant.