Who is the Bounty Hunter on the Star Wars: The Old Republic loading screen?

As stated in the novel "The Old Republic: Deceived", her name is Shae Vizla, though Malgus often refers to her simply as "The Mandalorian".

http://starwars.wikia.com/wiki/Shae_Vizla

It's fitting that she's named since she single-handedly shut down Coruscant's defense grid and also took part in the attack on Alderaan :)

Malgus probably chose her for the attack since she had a very deep-seated hatred of the Jedi because her brother was killed by Jedi Master Aurei Eadon.