Who's that what is a regular 'guess the pop-culture' character challenge. The artist draws a picture of something known to geeks, and then challenges people to guess what it is. The person who gets it right in the most interesting way gets to pick the next one.
Today's is relevant to
40K fans. Remember, don't spoil it on the forums, email the artist instead.
Take a look here:
http://davoul.blogspot.com/2012/02/whos-that-what-monday-13th-february.html