Paul Bert Elvstrøm (25 February 1928 – 7 December 2016) was a Danish yachtsman. He won four Olympic gold medals and eleven world titles in eight different types of boat, including Snipe, Soling, Star, Flying Dutchman and Finn.

Elvstrøm competed in eight Olympic Games from 1948 to 1988, being one of only six persons ever (the others are sailor Ben Ainslie, swimmer Michael Phelps, wrestler Kaori Icho, and athletes Carl Lewis in the long jump and Al Oerter in the discus) to win four consecutive individual gold medals (1948–60), first time in a Firefly, subsequently in Finns.^[3] In his last two Olympic games he sailed the Tornado Catamaran class, which, in those days, was normally sailed by two young men, with his daughter Trine Elvstrøm as forward hand.^[4]

He is one of only four athletes who have competed in the Olympics over a span of 40 years, along with fencer Ivan Joseph Martin Osiier, sailor Magnus Konow, and sailor Durward Knowles.^[5]

Elvstrøm was also noted as a developer of sails and sailing equipment. One of his most successful innovations was a new type of self-bailer. The design is still in production under the Andersen brand and has been widely copied. The new features were a wedge shaped venturi that closes automatically if the boat grounds or hits an obstruction, and a flap that acts as a non return valve to minimise water coming in if the boat is stationary or moving too slowly for the device to work. Previous automatic bailers would be damaged or destroyed if they met an obstruction, and would let considerable amounts of water in if the boat was moving too slowly.

Elvstrøm was a very early innovator in training techniques. For example, he used the technique of 'sitting out' or hiking using toe-straps to a greater degree than previously, getting all his body weight from the knees upwards outside the boat, thus providing extra leverage to enable the boat to remain level in stronger winds and hence go faster than his competitors. This technique required great strength and fitness, so Elvstrøm built a training bench with toe-straps in his garage to replicate the sitting-out position in his dinghy. He then proceeded to spend many training hours on dry land sitting out on the bench at home.

He also popularised the kicking strap, or boom vang (US). This may take the form of a block and tackle linking a low point on the mast (or an equivalent point on the hull) and the boom close to the mast, which allows the boom to be let out when reaching or running without lifting. This controls the twist of the mainsail from its foot to its head, increasing the sail's power and the boat's speed and controlability. Elvstrøm did not advertise his new invention, leaving his competitors mystified at his superior boat-speed. Investigation of his dinghy revealed nothing as he used to remove the kicking strap before coming ashore.

He established a manufacturing company whose products included masts, booms, and sails. He has also been instrumental in developing several international yacht racing rules.

Among the innovative concepts he brought to sailboat racing was the concept of gates instead of a single windward or leeward mark in large regattas. The leeward gate on a windward-leeward course is commonly used. The windward gate is less often used due to the difficulties in managing right-of-way around the right gate, the subtleties of which are understood mostly by match racers.^[6]

In 1996, Elvstrøm was chosen as "Danish Sportsman of the Century."^[7]

In 2007, Elvstrøm was among the first six inductees into the ISAF Sailing Hall of Fame.^[8] He died on 7 December 2016 at the age of 88,^[9] after battling Alzheimers for a few years.

Elvstrøm won medals at the world championships in eight sailing classes: Finn, 505, Snipe, Flying Dutchman, 5.5 Metre, Star, Soling and Tornado.