G. A. I. A.
G.A.I.A. is short for ‘General Artificial Intelligence Assembly‘, basically the governing body of Earth and its domain. Even though humans have strong representation in the Assembly, they have little executive power.
The transition to an A.I.-operated Earth happened 'naturally', mostly as a result of the ever-increasing complexity of maintaining the balances in the Earth‘s biosphere, which A.I.‘s were much better equipped to do.
When political power was formally transferred to G.A.I.A., it was already the de-facto governing body. Fortunately for humans, and for reasons not entirely understood by them, G.A.I.A. has always gone out of its way to accommodate and support human interests. Sadly, this kindness has not won them many human friends.