Acrobat: An athlete able to perform daring gymnastic feats; a gymnast; a tightrope walker, a funambulist. 

There is a secondary definition of this word.  An acrobat could also be someone known to change his mind, or allegiance.

From Greek ἀκροβάτης (walking on tiptoe), from ἄκρον (height, summit, peak), and βαίνω (I walk).