Yooden Vranx was at one time the President of the Galaxy. After his death, he was replaced by Zaphod Beeblebrox.
He informed Zaphod that he should steal the Heart of Gold at its launch event, and was part of the conspiracy that also included Zarniwoop to achieve this.
Vranx came into contact with Ford Prefect and Zaphod Beeblebrox for the first time when they snuck onto his starship, waving toy pistols and demanding conkers.