Andrew Ng might be a bigger name overall, but in the domain of AI X-risk specifically the biggest names are Nick Bostrom and Eliezer Yudkowsky.
There's a reason why Sam Altman's twitter profile was "Eliezer Yudkowsky fanfiction account" last week. He's heavily disagreed with but was extremely influential.
Yeah, funny how all the current noise about AI x-risk started by begrudgingly acknowledging Eliezer's pivotal role in the topic (and being formative to beliefs of like half of the big names involved), but quickly dropped him from the conversation. I guess now it's the Big Boys with Money and Credentials are discussing how to handle this Totally New Problem.