Martin Sorrell’s holding company S4 Capital has reportedly bought Silicon Valley’s biggest independent agency, Firewood, for $150 million in its latest deal to form a digital global advertising powerhouse.

The advertising boss, who was removed from WPP last year, having led the creative advertising agency giant for 30 years is now building his next venture with S4 Capital.

As part of the acquisition, S4 will merge Firewood with digital production firm MediaMonks, who the ad firm acquired last July. The move aims to further deliver a “purely digital, first-party data-driven, faster, better and cheaper content and programmatic offer, according to the release.

Founded in 2010 by Juan and Lanya Zambrano, Firewood employs more than 300 people across seven offices in the Americas and Europe. The firm, whose clients include tech heavyweights like Facebook, Google and LinkedIn, takes an “embedded” approach to client work, pairing creative and strategic talent with brands’ internal teams.

S4 will gain access to Firewood’s client base as part of the deal, in which the company raised $123 million through a placing to part-fund the Firewood deal and to also build up a portfolio for future acquisitions.

With the deal near completion, S4 will have over 1,800 employees in 23 countries. Previous acquisitions in the last 12 months also include programmatic advertising firm MightyHive, which S4 bought for $150 million in December, and the influencer marketing agency IMA, which merged with MediaMonks in August.