Ronald Kay Getoor (9 February 1929, Royal Oak, Michigan – 28 October 2017, La Jolla, San Diego, California)[1][2] was an American mathematician.

Getoor's book on 'Markov processes and potential theory', co-authored with Blumenthal, became a reference on the topic.

With Michael J. Sharpe, Getoor defined the notion of 'conformal martingale',[5] which proved to be influential in potential theory, investigated the behavior of Bessel processes, last-exit times and excursions.

Starting in the early 1980s, Getoor studied stationary extensions of a given strong Markov process, with time extending to infinity in both directions, formulating a pathwise view of "time reversal" which became a key tool in his studies of the excessive measures of a Markov process.

The 'Blumenthal-Getoor index', a concept which characterises the nature of discontinuities of Lévy processes and semi-martingales, is named after him.