He cofounded the Machine Intelligence Research Institute, an organization focused on AI alignment, in 2000, way way before it was a trendy topic.

He's also partially responsible for popularizing ideas such as the orthogonality thesis and instrumental convergence.

> Isn't he just some random dude on the internet?

Not really, most random dudes on the internet were not researching AI alignment in 2000.

> Why do people care what he says?

Many people were introduced to the concept of AI alignment thanks to him, so they are naturally interested in reading his reaction to progress in the field.