Betelgeuse VII is the planet orbiting Betelgeuse that Ford Prefect was born on. Soon after this, a Hrung collapsed on it, and Ford and his father were the only survivors. They then lived on Betelgeuse V, another planet in the system.
Ford's father named him in the language of Betelgeuse VII, but Ford never learnt to pronounce this name, which led to him being nicknamed Ix by his schoolmates, which meant "boy who cannot satisfactorily explain what a Hrung is, nor why it should choose to collapse on Betelgeuse VII".