Gottfried Wilhelm Leibniz, German philosopher at XVIII century noticed: living creatures are capable of doing work and almost called this phenomenon vis viva which is translated as "living force". Later, at the beginning of XIX century, doctor Thomas Young, watching the sailboats from the English Channel coast, rightly observed that the wind easily carries the ships, without being a living creature. He probably loved Greek more, so Hellenic words "a repository of work" transformed in term energy which is still used nowadays.
Energy unit in the SI system - Joule, named after an English brewer, James Prescott Joule, who in the course of dark ale manufacturing has found that it requires 778 foot-pounds of work to heat one pound of water by one degree Fahrenheit (1 Btu) and thus found correspondence between the kinetic and thermal energy. (Traditional British unit foot-pound is the work that is needed to raise 1 pound weight on one foot against the force of gravity)
One foot-pound equals 1,356 joules. And one calorie (the amount of heat required to raise the temperature of one gram of water by one degree Celsius) is equal to 4.18 joule.
To convert one unit of energy to other we offer you the following calculator: