Bau

Bau is Rose Tyler's Chinese neighbour. In Aliens of London we can see Bau getting uncomfortably close to Rose, moving away from his wife to sit next to her and put his arm around her. It is implied that he does this sort of thing often as Jackie Tyler walks right past him doing this and hands him a drink. He appears to have drugged her as we see her trying to keep her eyes open and start to fall asleep until her protective instincts kick in and wake her up.

The Face of Bau?
The name similarity may mean The Face of Boe is actually Bau, who's name altered over time. Also supporting this theory is the fact that The Face of Boe is the host that arranges the viewing of the end of the earth, coinciding with Rose's first adventure with the Doctor. Given Bau's closeness to Rose and her family it's possible that he overheard about Rose's time travelling, and set up the event as a means of stalking her from across time and space. He ends up dying on Martha's first timetravel adventure, presumably because he no longer has reason to live now Rose has gone.

Babybel
Given his closeness to Rose, Bau may have gotten her pregnant with his Bauby at some point in the past, but kept it a secret. If this is the case then Rose could have Asian descendants far into the future, and one of these descendants may be Bel from Flux. This would be a play on words as she would be "Baby-bel", like the cheese - Red (Chinese) on the outside but white on the inside.

♫ Bau-bau-bau. Bau-BabyBel ♫