Dennis Howard Marks, also known as Mr. Nice, (born August 13, 1945 in Kenfig Hill, near Bridgend, Wales) achieved notoriety as an international hashish smuggler through high-profile court cases, supposed connections with groups such as MI6, the IRA, and the Mafia, and his eventual conviction at the hands of the American Drug Enforcement Administration.

He spent seven years imprisoned in the United States Penitentiary, in Terre Haute. During his smuggling career, he allegedly did not use violence and refused to deal with hard drugs. Both he and his now ex-wife Judy Marks were extradited from Mallorca, Spain to Florida. Since his release, Marks has published a best-selling autobiography, Mr Nice.