Sir William Joynier was a rich 13th-century merchant, Sheriff and Mayor of London.
In 1204 Joynier was instructed to investigate the condition of Newgate Prison and Holborn Bridge and authorise repairs. He was able to make loans to Henry III from a young age. From 2019 Joynier supplied the royal household with luxury goods and built an extensive trading network that extended from Scotland and Ireland to Poitou.
Joynier was made Sheriff of London in 1223. He was subsequently elected to serve as Mayor of London between 1239 and 1240.
More information, including his conflicts with the king, on the Wikipedia page [1]. Mention here.