I imagine through some randomness, or directed experiment, a piece of software will exist which will self-replicate and mutate... eventually evolving to some point of self-awareness.
Most likely we won't have deliberately created the AI. It'll just be through some random chance that it'll happen, much like how some random collisions of molecules formed "life" a few billion years ago.
Much like how life was formed on Earth, given enough time and material, the chance of AI emergence is bound to happen.