He doesn't seem to do anything, but was wearing the same black and white suit when I last saw him. He was around this point 51.5004, -0.136213 when I spotted him and was travelling towards Richmond, but nipped off the Tube before I could see where he was heading.
A family sitting near me, saw me taking pictures, so they looked round and then started speculating as to why he might be wearing the mask.
The mother told her kids that he might have had a strange skin condition. It was a little too early in the day for him to have been going to a Halloween Party and there was just something very casual about him, as he checked his iPod, as though he travelled in the mask quite often. When I saw him before it was a weekday at about 8.30 in the morning.
Anyway, if you've seen him, know him, or indeed are him, please let us know in the comments. Any theories as to why he's wearing the mask would be much appreciated.