Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in 6,420 of hydrogen (~156.25 ppm on an atom basis). Deuterium accounts for approximately 0.0156% (or on a mass basis: 0.0312%) of all naturally occurring hydrogen in Earth's oceans, while the most common isotope (hydrogen-1 or protium) accounts for more than 99.98%. The abundance of deuterium changes slightly from one kind of natural water to another (see VSMOW).

The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common hydrogen isotope, protium, has no neutron in the nucleus. The deuterium isotope's name is formed from the Greek deuteros meaning "second", to denote the two particles composing the nucleus. Deuterium was discovered and named in 1931 by Harold Urey, earning him a Nobel Prize in 1934 after the discovery of the neutron in 1932 made the structure of deuterium obvious. Soon after deuterium's discovery, Urey and others produced samples of water in which deuterium has been highly concentrated with respect to protium, a substance popularly known as heavy water.

Daniel Dingel is a controversial Filipino engineer who claims to have invented a “hydrogen reactor” - a device which he claims to have used to power a water-fuelled car.

Dingel says he began working on his hydrogen reactor in 1969, and claims to have used the device to power his 1996 Toyota Corolla. Dingel explains that his invention splits producing hydrogen from water in an onboard water tank and does not produce any carbon emissions. However, he has never revealed the secret to his invention. In an interview with the Philippine Daily Inquirer, Dingel said that he would willing to reveal the secret of his invention if the buyer would hire 200 Filipinos and their families.

Dingle is known as a vocal critic of Filipino government officials and scientists who have refused to support his invention. The Philippines' Department of Science and Technology, in turn, has since declared his invention "a hoax."

In November 2000, Dr. John Ding Young of Formosa Plastics Group (FPG) sought Dingel out and, convinced that the invention was genuine, signed a “preliminary understanding” with him for several projects. He aims to have business partners to get an "international patent" and to commercialize his technology.