This is called putting a character to model: Having a certain perspective and facial expression given and trying to make it look like a specific character. It's the skill needed by storyboard revisionists, who get the rough boards and have to elaborate on them.

As you can see, I'm not very good at these yet... The characters may all be recognizable as the same guy even without color, but the different drawings seem to have different styles to them when they should be uniform. Some of them even look as if drawn by different artists. Also, it's unfair since this character archetype is more or less all I draw; if I had to do this with an old woman or a baby I'd look like a 1st grader with crayons.

Granted, these were surprisingly quick and more straightforward to do than I expected but I guess it's easy when you can draw whatever expression you want. Actually making use of this in practice is much harder. Still, it was a nice little exercise to draw in the middle of the night.