Alright, let's get this going.

These characters are each meant to hit certain scifi subgenre notes.

Here's the hardnosed mercenary.

A mix of:

Jugger Grimrod <3, the original green badass from the old Alien Legion comics,
some Maximillian from The Black Hole,
Ralph Bakshi's Wizards,
Oddworld
C.O.B.R.A.
HALO
Stormtroopers
Judge Dredd
and any generic space marine imagery

There's a kind of sci-fi fan that gravitates to the overcompensating fascist hardshell machismo angle, and takes it very seriously. This is that guy. If the character strikes a chord with you, check out the list of references, you'll probably enjoy something there :)

Too much Cold War with the Soviet Union produces this aesthetic.

[NOTE: The first pass is to double the size of those thumbnail silhouettes and make decisions about the detail that was initially just suggested.]