Who is Salt?

I'm going to check out Angelina's new movie "Salt" tonight which I hope lives up to my expectations. I have been seeing the trailor and posters around the cinema for months now and have been interested in finding out who this "Salt" character is. I must admit though I have a love/hate relationship with Angelina. I used to love her, then I couldn't stand her, now with "Salt" I feel I want to embrace her once again. Come back later tonight and I will give you my verdict if "Salt" sizzled or let a sour taste in my mouth.