Someone engaged in a dangerous but potentially rewarding adventure.

Or paper nautilus; Octopus living in the open sea, genus Argonauta. The female of the common paper nautilus, A. argo, is 20 cm/8 in across, and secretes a spiraled papery shell for her eggs from the web of the first pair of arms. The male is a shell-less dwarf, 1 cm/0.4 in across.

(Classical mythology) One of the heroes who sailed with Jason on the Argo in search of the Golden Fleece.
Companion of Jason in the Argo; any heroic sailor; paper nautilus.