If not everyone has to be a mad scientist or construct:

One you can always need in these settings is The Veteran. There are several varieties of veterans, all sharing the common trait that they were in a war, most likely one that went badly and longer that it should have, and that they are now older men (the archetypes is at least around 40) and highly capable in their chosen field.
The Veteran knows basic battlefield medicine, how to organize a squad of people, how to tell slightly disgusting, but fascinating anecdotes, he can shoot, fight unarmed, knows the basics of stealth, and has a strangely detailed knowledge of the customs and geography of distant lands.