You may have heard of him when James Cameron's ocean exploration was discussed. Or via the movie, "The Life Aquatic". His ship, the Calypso, is a memorable name. He is probably "the" most famous or biggest household name regarding nautical exploration from 1970-2010? (whenever Cameron entered the zeitgeist. & I guess Cameron's been to the Titanic 33x??). I assume Costeau would be the go-to for a picture + blurb in a K-8 textbook when discussing ocean ecology etc. Maybe he's more of a Gen X or baby boomer figure. Maybe he was part of the "save the ozone layer/ocean/reduce/reuse/recycle" state-sponsored propaganda campaign of the 80's/90's.

The Jane Goodall of ocean voyaging. Probably less familiar than Goodall to a layman.

You'd probably remember Glomar Explorer, Exxon Valdez, Cousteau, maybe Kon Tiki, maybe some offshore oil drilling incidents.

Then you just have to assume "scuba"