Funambule, from Lat. funambulus: funis, rope, and ambulare, walk. Tight rope dancer.
I went to see Man on wire, the story of Philippe Petit, who performed a high-wire routine between the two towers of the World Trade Center in 1974. I highly recommend it, if only for his explanation of why he did it ("When I see three oranges, I juggle; when I see two towers, I walk") and his redefinition of the word "impossible": "It’s impossible, so let’s start working."