Most people that study AI existential risk specifically are studying it due to concerns about AI x-risk. So the list of relevant AI x-risk experts will be subject to massive selection effects.
If instead you want to consider the highest status/most famous people working on AI in general, then the list of signatories here is a pretty good summary. From my flawed perspective as a casual AI enthusiast, Yann LeCun and Jürgen Schmidhuber are the most glaring omissions (and both have publicly stated their lack of concern about AI x-risk).
Of course, the highest status people aren't necessarily the most relevant people. Unfortunately, it's more difficult for me to judge relevance than fame.
If instead you want to consider the highest status/most famous people working on AI in general, then the list of signatories here is a pretty good summary. From my flawed perspective as a casual AI enthusiast, Yann LeCun and Jürgen Schmidhuber are the most glaring omissions (and both have publicly stated their lack of concern about AI x-risk).
Of course, the highest status people aren't necessarily the most relevant people. Unfortunately, it's more difficult for me to judge relevance than fame.