I'm sure most of you gamers out there have played at least one of Valve's revolutionary Half Life series. As they've been some incredibly influential games, I decided to create a Gordon Freeman, Half Life's main character, Corky.
Here's how I did it.

Step 1: Supplies

Supplies:

1-2 Champagne Corks
Styrofoam
Thick aluminium wire
Card or thick paper
Brown fur or hair
Standard steel wire

Scissors
UHU glue
Craft knife
Needle nosed pliers
Super/Krazy glue
Brown, black, and orange Sharpies
Styrofoam cutter
Hammer
Wire cutters or metal cutting scissors
Pencil
Fine black permanent marker
Paintbrush
Orange acrylic/poster paint
Black and white, or grey paint
Orange pen

Also (forgot to include in photos):

Hot glue (most other glues will melt styrofoam)
Transparent plastic foil (from packaging)
Yellow pen

Step 2: The Head

Make sure that your champagne cork is completely blank on at least one side of the top half, so you can draw the face without having annoying writing all over it.
Use a permanent black marker to draw the eyes, nose, and mouth.
I did the hair before the rest of the face so I wouldn't position the beard and the eyebrows too high, but it wouldn't make a difference if you did it last.
For the hair, I glued wads of brown fur onto the top and sides of the cork, leaving a space where the ear should be. Then I trimmed it all down to the appropriate length and filled in gaps where you could see the cork with a brown Sharpie.
Now draw on thick brown eyebrows as shown above. To draw the beard, plan it out with a soft pencil, then go over it with the brown Sharpie.

Finally, for the glasses, draw the frame out on a piece of transparent plastic foil (from some packaging) and cut it out. Make sure that it fits the face. Don't attach the glasses yet though, because they might get ruined during the other steps.

Step 3: Hazard Suit

Making a Gordon Freeman Corky was really experimental, as I had to figure out a way to make the Hazard (HEV) suit. Styrofoam worked, but may not have been the best solution as some of the edges easily crumbled off. I can't think of any good alternatives though.

To make it using styrofoam, hot glue pieces around the entire bottom of the cork, making sure it's fitted as tightly on the cork as possible. Then use a styrofoam cutter to cut away at it until it is the correct shape. Use a craft knife for details. Try to use a sharp knife, as blunt blades will tear the styrofoam, creating jagged edges.

The shape of the styrofoam in the end should look similar to mine above. Leave a slanted flat part on the front, but slant it slightly less than I did.

Step 4: Painting

Cut out a small rectangle of card that will fit the slanted flat area, and draw on a yellow lambda logo on an orange background. Glue it onto the flat area, and paint the rest of the cork as shown above. Finally, outline the details with a black permanent marker.

Step 5: Crowbar

For Freeman's iconic crowbar, use some thick (but soft) aluminium wire. Cut about a 4.5cm piece, then use a hammer to flatten the ends. One side only needs to be slightly flat. For the end that's flattened most, use wire cutters or metal cutting scissors to correct the end (after hammering it it may have become rounded instead of straight) and make a small cut down the middle. Then, use some needle nosed pliers to bend each end as shown above.

Finally, use permanent markers (Sharpies worked well) to give the crowbar its painted texture. I used red first and then added the black while the red was still wet.

Once it's dry, attach the crowbar to the side of the cork by pinning it down with a short piece of wire. Now you can also add the glasses. I did this with some Krazy glue (only apply glue to the nose and under the hair).