Or Réné Descartes in the 17th century. The fundamental nature of res cogitans so to be conscious... if that rings any bells. :)

It's also an idea that few philosophers of mind agree with at this point. Gilbert Ryle did a pretty good job of showing that the mind-body problem is a pseudo-problem [0].

[0] https://www.amazon.com/Concept-Mind-Gilbert-Ryle/dp/02267329...