Lars Onsager was a really smart man who studied the way that things like water and electricity move around. He found out some really cool things that helped us understand how electricity works.
Think of it like this: When you have a glass of water and you stir it around, the water moves in a certain way, right?
Well, Onsager found out that when you have small electric charges that move around, like the way electricity works in a lightbulb, they also move in a certain way. He figured out how they move around and why they move around that way.
Even though it might seem boring to some people, this helped us understand a lot about how electricity works in everything around us, like in TVs and computers. People still study what Onsager learned today because it was so important!