Who is Lord Krishna?

Krishna, the one who at the beginning was no one, just a simple charioteer. "He told his charioteer: 'Krishna, halt my chariot between the armies!'" But he is a type of charioteer that everyone would like to have! After Arjuna is in the middle of the battlefield, Krishna becomes something different...

Arjuna asks him things, and he starts calling him Lord Krishna. Lord Krishna starts talking to Arjuna about a lot of stuff he doesn't understand at first. He talks about honor, respect, that he should go to the battle, about Karma-Yoga, some knowledge he should have, knowledge of the absolute, being perfect, the universal form, devotion service, nature and taking care of it, the Yoga of the Supreme, divine and demoniac natures, the divisions of faith, and more complicated topics. This Lord Krishna knows about what he is talking about, and he knows it well. 

He also talks about no one ever dying or being born, just hanging around in the form of soul and taking human bodies occasionally. But there is something that caught my attention, and it is the setting of the Bhagavad Gita. They are in the middle of a battlefield. What I interpreted was that Arjuna needed help to go to the battle, he wasn't sure. He asks Lord Krishna for help, and here is where Lord Krishna starts preaching to him all the topics named above. I think the battlefield setting was just an excuse to create a good place where somebody needed help, because it has no other purpose in the story.