[Facts] Re: Is Endeavour really an existing male English first name?
Actually, "endeavour" (or, the American spelling of "endeavor") is a noun as well as a verb, meaning: "a conscientious or concerted effort toward an end".
I wouldn't be surprised that it may have been used as a name in the past, as the Puritans were well-known to give their children "virtue names" such as Solace, Confidence, Discretion, Perseverence, etc. I don't believe the Quakers, though, were as much inclined to use those types of names.
The reference to Captain Cook has to do with his ship, which was named The Endeavour.
-- Nanaea