As the sibling comment by idkwhatiamdoing says, Geoff is Geoffrey Hinton: «Geoffrey Hinton leaves Google and warns of danger ahead»
https://news.ycombinator.com/item?id=35771104Yoshua is Yoshua Bengio: «Yoshua Bengio: How Rogue AIs May Arise» https://news.ycombinator.com/item?id=36042126
LeCunn is replying to Max Tegmark: «Ask HN: What is the apocolyptic scenario for AI “breaking loose”?» https://news.ycombinator.com/item?id=35569306 «Max Tegmark: The Case for Halting AI Development | Lex Fridman Podcast #371» https://www.youtube.com/watch?v=VcVfceTsD0A