A Series D Backer is an investor who provides funding to a startup during its Series D financing round. This round typically occurs after earlier rounds (Series A, B, and C) and is aimed at helping the company scale further, enter new markets, or prepare for an initial public offering (IPO).
Synonyms: Series D Investor, Late-Stage Investor, Series D Funding Participant, Series D Capital Provider

Series D Backers usually come in when a startup has already demonstrated significant growth and market traction. They invest substantial capital to support late-stage development, product expansion, or to boost the company's valuation before going public or being acquired.
These investors often bring more than just money. They can offer strategic advice, industry connections, and help with governance. Their involvement signals confidence in the startup's potential, which can attract additional investors or partners.
Large venture capital firms, private equity funds, and sometimes corporate investors participate as Series D Backers. For instance, a tech startup expanding globally might secure Series D funding from a major VC firm known for backing late-stage companies.