I nominate "The Tanzanian Devil". Though on a more serious note. Why don't we wait til he actually has play a few games for the Rockets before jumping the gun and developing nicknames...
One doesn't get a nickname in the NBA unless he can score a bucket per game. Thabeet is a project and long term project. Don't get your expectations too high.
You totally beat to the the "Avatar" name.. i like it! I'm not good at photoshop, but here's a good comparison!