Who's This? The boat captain character at the top of Who's Who vol.IV, page 11.
How you could have heard of him: Couple of bronze age appearances (including 'Tec #500), and sort of his head once during Crisis (Swamp Thing #46), but his last real (story) appearance was a reprint in a Best of DC Digest in 1982. So you probably only remember him from this Who's Who entry.
Example story: Star Spangled Comics #119 (1951)
Among the techniques he's brought along, for example, is an explosive harpoon. Are you telling me these are safe and humane?
Wikipedia has some "citation needed" hogwash about Compass working the Martian Manhunter on a boat trip, and later working with the Justice League. I'm not sure who the Wiki-ist is confusing Mark Compass with... Any ideas?
Who else? I don't need to go far. Captain Compass is at the top of the page, and who's at the bottom? Captain Fear, a more recent sea-faring character, but not very well known either! Hope you like the open seas, because I'm not ready to come to shore yet!