Here is my tutorial on drawing a zombie portrait. For my subject I decided to use one of my childhood favorites Mr. T. I have done many of these kinds of portraits in various mediums but this particular drawing was done using color pencils and paint markers. Below I have listed everything that I used.

Materials:
Color Pencils - black, red, purple brown, yellow, blue and magenta.
Paint Markers - black, red, yellow, brown and orange.
Sketch paper - unfortunately I only had my charcoal sketch pad available, hence the visible lines appearing in the shaded areas.

Step 1: Step 1: Find a Subject to Transform

First step, find a picture of someone you would like to zombify. I just did an image search and settled on an image that I liked.

Step 2: Begin Drawing

So next you want to start drawing, if you are lacking in artistic ability, no worries you can always trace your subject. The general idea is to get the main features and silhouette of your subject.
Start off using a pencil and creating soft, light lines.
I started out drawing an oval shape and marking off my center lines for my eyes, mouth, nose and hair line placement. As well as the body and chains.
Next I drew the hair, ears, eyes, nose and mouth, I marked some lines here and there around the face just to get a feel for certain ideas that I may want to incorporate later.
Once I got my features I then began to darken the lines I wanted to keep such as the outline and details in the eyes, nose and mouth.
Last I'm left with a rough sketch of Mr. T.

Step 3: Time to Zombify

So once you are content on your sketch we begin making the subject into a zombie. I like to use references for this part using google search and my various books on anatomy to get a good idea of creating a under structure that looks like the real deal.
For this drawing I wanted to make it look like Mr. T was scratched across the face so I made three big, finger like scratch marks, one of which torn down his eye lids, exposing his whole eye and split his lip open, exposing his teeth. I also added some sore spots along his head.
Looking at the anatomy of the face pictures helped greatly in determining muscle structure and teeth placement.
When doing the skin tears I like to create jagged, warbled lines to make it look more like torn skin.
(The lines along side Mr. T's head by the way was an idea to draw his feathers but later I decided to rule this option out.)

Step 4: Outlining

Once you are comfortable with your zombie look we begin the outline. This will be done either using a black fine point pen or marker. You outline the main head and body silhouette.
Next, we do the hair which I basically drew by doing many little circles and c's over and over and over lapping one another until it was very black with few specs of white showing through. You'll notice that there are spots on his beard and mohawk that are left partially scribbled. These are areas that I intend to leave like this because I plan on coloring in blood and want these areas to look more like blood splatters.

Step 5: Coloring Time

Now we begin our coloring. I start out by outlining the facial wrinkles and definining lines on Mr. T's face with my fine point brown paint marker.
Then you want to color in the skin. I wanted to make the main part of his face lighter due to being a zombie.
I then lightly shaded in the skin while darkening the skin in areas of wrinkles, hairline and mouth area. Here I used just brown for the skin and added purple veins which I drew lightly in but enough to just poke through the brown. I kept the vein work around the corner eyes, and mouth area and had longer veins stretching around the head.
I lightly colored in around the eyes and cheek as well as the lips with purple and magenta to add the decayed look.
Next I shaded in the scratches and sores with pink, purple and magenta, shading in more heavily around wrinkles and muscles.
Last I went in with my red paint marker and added in the blood. I pooled blood spots on the corners of the scratches and sores and made blood splatters along the face.
Around the mouth I made blood spill down his mouth and chin but also made the blood splatter outwards as well as on the teeth to make it look like he has been biting some people.
I outlined the lines that were meant to be muscle in red to make them pop. I also decided to make his ear look torn on the bottom of one ear and bloodied on the other but with only one earring.
The eyes were done using a fine point red paint marker. I drew many little veins around the eye and an red circle outlining what was the iris.

Step 6: Finishing the Details

Here I began just going back over my lines, especially the blood to darken any lines which were too light. I also added more shading to the skin and exposed parts.
Then I started working on the lines for the chains. The bigger chains were rope chains, so I used a reference picture and began drawing the lines in. Once I had the general lines done I began to go over the lines using a yellow fine point paint marker. I then erased all unnecessary lines left from my pencil leaving behind only the yellow outline. I then colored in the chains all in yellow and outlined the inner lines in a light orange all using my paint markers. I later decided to out line my chains in black just to make them pop out more. I then added blood to the chains, I made it look like it was spill over from his chin and mouth so it is heavy on the middle with splatters along the outer edges. It is important to keep in mind dimensions of the chains and to color accordingly so that it makes it look like blood on chains. This can be tricky because not enough attention to this detail could leave it looking like a big red blob.

Step 7: You Now Have a Zombie

Last I colored the shirt in black with the paint brush leaving around some lines to make it look like clothes which I colored in with a black color pencil and shaded a light blue background.

I've added some of my other zombie portraits just to give you some extra ideas to play around with.

I have made many portraits and have always enjoyed just playing around with the possibilities. I hope this gets some ideas stirring and hope that people share their own zombie portraits.