I'm confused about MRCAs

Why isn't the Last Universal Ancestor the first organism on Earth? It had to be bred from someone, right? So how come it's parent or another ancestor isn't the Last Universal Ancestor instead?

``Last'' as in ``most recent''.

Well the parent of the last universal ancestor would be next-to-last universal ancestor you see.  The first organism on Earth, assuming that its progeny survived and became us, would be the first universal ancestor, not the last universal ancestor.