AphexTwin is Richard D. James. Has also used the names Polygon Window and AFX.
These guys make crazy videos.
See http://allmusic.com/cg/x.dll?p=amg&sql=1APHEX|TWIN (BrokenLink 2005-04-11)
Actually, he makes (used to ?) really interesting electronic music. The videos in question are made by the equally mad and talented Chris Cunningham.