Robert Jeremy Goltho Grantham CBE (born 6 October 1938) is a British investor and co-founder and chief investment strategist of Grantham, Mayo, & van Otterloo (GMO), a Boston-based asset management firm. GMO had more than US$118 billion in assets under management as of March 2015. GMO has seen this number half to US$65 billion in assets under management as of Dec 2020. He has been a vocal critic of various governmental responses to the Global Financial Crisis from 2007 to 2010.Grantham started one of the world's first index funds in the early 1970s.

In 2011 he was included in the 50 Most Influential ranking of Bloomberg Markets magazine.

Grantham built much of his investing reputation over the course of his career by identifying speculative asset bubbles as they were unfolding. Grantham avoided investing in Japanese equities and real estate in the late 1980s during the peak of the Japanese asset price bubble,[11] and avoided technology stocks during the Internet bubble of the 1990s. A decade later, he limited his exposure to the housing bubble. Writing in Kiplinger in 2010, Elizabeth Leary noted that many of Grantham's predictions can be confirmed by analysis of his past newsletters.[12] In a 2021 interview, Grantham distinguishes between identifying overpriced asset bubbles (which he believes is not particularly difficult), and predicting when such bubbles will collapse (which he admits is impossible, stating only that asset bubbles will eventually end at an uncertain future date). Grantham also acknowledges his strategy can underperform market averages for years, testing the patience of his clients, but he asserts that his strategy has always paid off long-term by avoiding overvalued assets.[13]

In GMO's April 2010 Quarterly Letter Grantham spoke to the tendency for all bubbles to revert to the mean saying:

свернуть