The most effective character description, is the one your reader creates for themselves. Your job is to provide enough clues for your reader to create their own character, based on yours.
Most readers will identify themselves as the central character, even if this is blatantly opposed to the description you give. One of the joys of reading is that you vicariously live another life through the character in the novel: you become that character and experience their emotions and action through the story.
Don’t try too hard to pin down your character’s physical appearance, other than a sketchy outline – make it easy for your reader to imagine themselves in the central role.
Is your character black or white? Unless the colour of their skin is integral to the story, why risk alienating a section of your audience by defining their skin colour? Let the reader decide.
Concentrate instead on their characteristics (personality), emotional traits, and actions. These are the things your readers really want to explore, i.e. in a safe environment, what does it feel like to be a psychotically murderous megalomaniac. They are also the things that ultimately define your character, whatever their physical appearance.
As to how you write that character, concentrate on ‘showing’ characteristics, emotions, and actions, rather than ‘telling’. Drip feed it all in, one scene at a time.