The Last Last Question is the name of a collection of extra-multiversal objects used to communicate with aliens who supposedly created this universe.
They are basically one among infinite chains of sentient universes, each more complex and more intelligent than the last.
Aside from the fact that they put a domain wall around our universe, they are simply just creatures who ran out of things to learn within their respective universes and concluded that the only way to learn more things is by creating a better universe, such as this one.
In time, we will be just as advanced and we will do the same, and the ones we will create will do the same, ad infinitum. This never-ending cycle of creating and learning universes is essentially, God.
I couldn't agree more.