Transgenic86 AKA DemonStrate.
I just linked to the whole playlist. Can be watched in order from the beginning to the end. It's amazing. (if you know Portal
)After a LONG break after chamber 17 v2 he actually returned and did a few more maps, last video so far finished escape 00 in five seconds. Escape 01 and Escape 02+GLaDOS still remain, but I'm sure he'll do them soon.