When you're making an actor into another person you must alter his appearance so it fits  the new character. If the character is mean, kind, fat, thin or ugly you must change the actors own features to match this.
To be able to do this we use a lot of different methods such as wigs, false teeth and facial prosthetics.
All of these techniques have their own pages. On this page the most basic way of doing character makeup with light and shadows using greasepaint is explained.

Pictured: Ingvar Wixell as Falstaff 

When you're doing a highlight and shadow makeup you are really just using the actors own features to alter his looks by showing and hiding things that are already there.
Some actor once said that all parts are an insult, because the makeup artist always bring out the "bad" bits of the face when doing a character makeup.
Depending on what kind of stage you are working on the makeup can differ quite a bit.
If you're working on a small stage you have to put on makeup which is very subtle but for a big stage it can look really grotesque in person but great on stage.
On the left you can see a very strong makeup that looked quite natural when he was on the dark stage.
For the shadows I use the colour "death purple" because I don't like it when people make shadows in pure brown or black as it looks totally lifeless.
For the highlights I use an off white colour which is mixed with the foundation.  

Pictured: Johan Schinkler as Daland in The flying Dutchman 

Character makeup can also sometimes be classical makeup's like the Peking opera masks or Japanese kabuki makeup.
These kinds of makeup are very hard for us in the west to understand and do correctly because they come from thousands of years of tradition.
Every colour and line means as much as a whole book of knowledge.
All we can do is mimic or do our own interpretation which is bound to be wrong.
However, it is beautiful makeup's that all makeup artists often try to do.
Here you can see a stylized kabuki influenced makeup I did for an Opera.

Pictured: Ilona Andreasson in a test makeup for Aniara

Myself made up to look tired and sick

Theatre aging makeup on Lola Ewerlund