A Series D investor is an individual or entity that provides funding to a startup during its Series D round of financing. This round typically occurs after earlier rounds (Series A, B, and C) and is aimed at supporting further growth, scaling operations, or preparing the company for an exit such as an acquisition or initial public offering (IPO).
Synonyms: Late-stage investor, Series D funding participant, Series D venture capitalist, Series D backer

Series D investors contribute capital to startups that have already demonstrated significant progress and market traction. Their investment helps the company expand its market reach, develop new products, or strengthen its financial position before a major liquidity event.
Series D funding usually takes place when a startup needs additional resources beyond the earlier rounds. This can be due to slower-than-expected growth, new market opportunities, or the need to outpace competitors. It often signals that the company is in a mature stage but still requires capital to reach its next milestone.
These investors can include venture capital firms, private equity firms, hedge funds, or even late-stage venture investors. They tend to look for companies with proven business models and clear paths to profitability or exit.