The discovery of energy is not credited to one particular individual because there are several types of energy, and each was discovered by a different person at a different time. For example, Michael Faraday discovered electromagnetic energy and Benjamin Franklin discovered positive and negative electrical charges.
Once Franklin discovered positive and negative electrical charges, he used his discovery to invent things like the lightning rod. Faraday, who lived from 1791 until 1867, used his knowledge of electromagnetic energy to invent the dynamo, which converted motion into electricity.
Thomas Edison discovered electric waves in space. Using his discovery along with other technology, he invented things like an improved light bulb and an X-ray machine. Another scientist, Nikola Tesla, used his discovery of alternating energy current to invent an electric transformer and an improved X-ray machine.
Many scientists have had the things associated with their discoveries named after them. For example, the watt was named after James Watt, and the volt after Alessandro Volta.
Throughout the years, scientists who study the different forms of energy work on improving the idea of others who came before them as more knowledge and technology became available. The largest form of energy, the energy created during the formation of the universe was first discovered by Belgian physicist Georges Lemaitre in 1931.