It's no secret
TRAPJAW is one of my all time favorite characters. Something about his frankensteined, robo-body really clicked with me when I was 7 years old. And nowadays, I think there's just an interesting mix of characteristics (sharp teeth, bullet-shaped head, jolly roger belt buckle, bionic joints, green face, blue skin, etc.) and geometric shapes that are fun to play with design-wise.
Here's a half-hearted attempt at documenting process. Enjoy!

Here's a sketch! Ran out of paper for his foot! Cropped his hook hand for some reason! Written note of head size doubts!

I cleaned up and colored this image in Photoshop with it's vectors - which I love 10 times more than illustrator. I probably still like doing vector work in Flash the most, but Photoshop has so many other features. I started with his head here blocking in solid shapes for his noggin and jaw. I went as far as cleaning up some lines and defining his face because I wasn't sure where to go artistically. Once I felt good about the head, once I felt like I had a direction, I continued blocking.

Vectoring up his upper body. Scribbling in some muscles.

Lower body vectors! And some layers turned off!

Added a vector robo-arm and the big change here is lengthening his legs. Guess I liked that option over shrinking his head.

Details! Shadow passes and any sorta line work was done with a Wacom. And lookit that - more adorable splotches next to his head!

Adjust colors, some abstract sorta hilites, call it done.
BONUS image! Here's a another fatter, messier, Trapjaw!