Infrared radiation wasn't "invented" by a single person. It's a natural phenomenon, a type of electromagnetic radiation.

However, the person credited with discovering infrared radiation is William Herschel in 1800. He conducted an experiment using a prism to separate sunlight into its different colors. He noticed that the temperature was highest just beyond the red end of the visible spectrum, indicating the presence of invisible radiation.

So, while infrared radiation always existed, Herschel is the one who first identified and characterized it.