> He's considered the father of rationalism

[citation needed]

Even for this weird cult that is trying to appropriate the word, would they really consider him the father of redefining the word?

I think that claim would be pretty uncontroversial among people who consider themselves rationalists. He was extremely influential initially, and his writing kicked off the community.

Less metaphorically, he was a prolific, influential blogger. His early blog posts are collectively known as "the Sequences" and when people asked what rationalism is about, they were told to read those.

So the community itself gives him a lot of credit.

Not of the philosophy (I'd attribute that to Popper), but of the modern movement.

The article you're reading is from the unofficial rationalist magazine and the author is a prominent rationalist blogger, so they (and I) obviously don't consider it a cult. But, yes, Yudkowsky is absolutely considered the founder of the modern rationalism movement. (No relation to the philosophical tradition also called "rationalism". Modern rationalism is mostly actually just empiricism.)