When Professor Kleiman and a team of colleagues he had assembled were hired by Washington State in 2013 to help implement a law that legalized both the medical and recreational use of marijuana, he bombarded officials with so many suggestions that even he applied to himself a famous characterization of Senator Hubert H. Humphrey: “He’s got solutions the rest of us don’t even have problems for.”

The full name of Professor Kleiman’s consulting company is Botec Analysis Corporation; “Botec” stands for Back of the Envelope Calculation. While the name belied his exacting and encyclopedic approach to policy research, it acknowledged the ambiguities of an underground economy in which illegal drug trafficking generates millions of dollars.

In Washington, he startled state officials by predicting that loosening prohibitions on the sale and use of marijuana would initially raise the costs of law enforcement, because the police would have to deter illicit dealers who would otherwise undermine the fledgling legal market.

“What distinguished him was his ravenous and wide-ranging intellect and his commitment to sharing it,” Dr. Sally Satel, a psychiatrist, friend and colleague in Washington. D.C., said in an email. “There are lots of brilliant people out there, but what I remember most and valued most and will miss the most is how generous he was with his own ideas and how gleefully, sometimes brutally, he’d help you dissect yours.”

Mark Robert Kleiman was born on May 18, 1951, in Phoenix to Dr. Allen and Jeanette (Albert) Kleiman. He was barely a teenager when he quirkily adopted “A” as an extra middle initial, from his mother’s maiden name, so that all four initials would spell Mark.

His mother taught economics and social science at, among other institutions, the historically black Morgan State University in Baltimore, where Mark grew up. His father was a surgeon.

Mark evinced a passion for public policy early. At 14, he was a page at the Maryland State Constitutional Convention. At 17, he was writing speeches for Parren James Mitchell, the first black congressman from Maryland since Reconstruction.