Planet Ubuntu is full of hilarious Chuck montages. Here two examples:
Why is that? How did Chuck become an Ubuntu meme?
Note: This question is not meant to be a Chuck montage collection. It is a real question!
Chuck is Chuck Short - ~zulcss - I believe he has become famous due to his love of WHAM, Boy George and the Village People and is leveraging his fame to teach people the Ubuntu Dance (as seen below).
This (community-wiki) answer will serve as a reference for all "Chuck" pictures: