I'm pretty sure this guy is based off of Morgan Freeman, just a hunch... Anyways, since I did that image of Robotnik I was compelled to explore Nate more. I've done so in the past, but I thought it would be interesting to draw a younger Nate to compare to the old one in present day.
You will notice a lot of images that take place in Ivo's (Robotnik) youth show him interacting with Nate a lot. In fact, it is Nate who surgically repairs his eyes and it is Nate who becomes his physical therapist.
At the time Robotnik looses his eyes he's around 10-13 years of age; Nate's around 23-25. Robotnik views Nate in a complex manner, that of a friend and a servant. Although he doesn't have much empathy that one would consider normal, Ivo does have a habit of expressing it towards him, at least in their youth.
// END SPOILER //
Anyways, both Nate and Ivo are Overlanders. Unlike Robotnik, Nate has more human proportions while Robotnik shows traits more common to Overlanders, that is, anatomy being way out of proportion in comparison to one another. This is due to them being partially composed of animal DNA and are the human equivalent to the Gremlin race (beings like Lupe, Big, Rouge, ect)
I haven't decided wether or not Nate will have more dwarf like proportions or not. Snively was intended to fill that role (for the sake of anatomical variety) but I think Nate looks a bit too human, and could benefit from some alterations in his anatomy to make his race more apparent.
I should also note that all Overlanders have cool colored mouths. With tongues and gums ranging from blue, purple. and black in appearance. I don't why I'm sharing this, has no significance considering this is colored. That being said I felt as though it was an important minor detail.
These sketches right here are a few months old. Anatomically I like them, especially the top head, reminds me of the 90's sprite of Robotnik in his ship.
Image from here.
Call me nostalgia based, but I much prefer the older Japanese design of Robotnik. I think it's design left more to the imagination when I was a kid. But I also liked the 90's version of him to from SAT:AM.
My version of him is aiming between a cute and cuddly but nightmarish dictator with a child's mentality.
The major characteristic about my version of Robotnik is that you never see his eyes. As a child, he wears glasses and the lighting is always such that his eyes are hidden by the shadow reflection of his lenses. That and he's "eyes" you do see are very mechanic and make noises like a camera when focusing or changing modes from daylight, infrared, or night vision. I've always had a fascination of showing the deadness eyes possess when seen from a mechanical standpoint. And the design of my yes were inspired by the squiddies from the animatrix and Hal 9000.