I actually painted this prior to the release of Avengers Endgame. The anticipation was running high and I wanted to visualise a moment that I really hoped would take place; Cap proving his worthiness - lifting Mjolnir and shouting "Avengers assemble!". I was delighted when I watched this dream scenario unfold on the big screen before me at the midnight release of the film.
An unfortunate drawback of this spot on prediction was a good deal of angry messages saying I'd spoiled a key moment in the film!
I usually just scribble these down on a sheet of A4 printer paper with a pencil.
The first sketch was too stiff, I was trying too hard to have the shield design showing and it compromised the pose - which already wasn't dynamic enough.
I was quite pleased with the second pose, but I really wanted to be able to see the front of the shield. The third pose was a bit too extreme.
Finally, the pose on the right is the one I settled on - it was a good balance of being dynamic while still showing the shield design.
Gathering pose and lighting reference. I've had this Body Kun reference figure for a little while but haven't used it a great deal, I wanted to take some posed shots of it just to help inform the proportions of the finished drawing.
After a fair bit of searching I found a reference photo of Cap himself - Chris Evans - from a close angle to what I needed. I used that to then alter the expression and rough out the head and helmet.
From there I painted directly on top of the thumbnail sketch to mock up the body and piece as a whole. This stage is very quick and rough, I'm just establishing the forms at this point - they'll be refined later.
As you can see here, I initially played with the idea of a comic-book style speech bubble shouting the iconic "Avengers assemble!" but eventually abandoned that.
Continuing on from the last step I start to figure out in more detail the placement and proportion of the body and the costume. On a separate layer I paint a rough guide for Cap's muscle structure, this helps inform how the costume sits. On the right you can see the painting starting to take shape.
Painting in the details using a Wacom Cintiq on Adobe Photoshop
Animated GIF showing the process - from thumbnail sketch, to rough mockup, to final art.