"The other name of Captain Kidd, world-renowned pirate. For years after his death, songs and legends of his life inspired many to chase rumors of his buried treasure across the seas."
—Persona 5 Royal compendium
William Kidd was a Scottish pirate and privateer in the 17th century. His early career was spent in the Caribbean, where he aided the besieged English colony of Nevis by ransacking the attacking French. In recognition of his actions, the King of England awarded him a letter of marque, granting him legal protection so long as he remained loyal. However, during a voyage to the Indian Ocean, his crew plundered a neutral ship without his knowledge, branding him an outlaw once more. Eventually, he was captured and sent to London, where he was tried and executed in 1701, the number printed on the persona's hood.
As time went on, William Kidd's reputation as a pirate became the stuff of legends and folklore, with many tall tales being told about his adventures, most famously involving him burying plundered treasure to protect it from his greedy associates.
William — alongside his un-evolved form — is one of the few Personas in the series based on a historical figure, rather than a figure from mythology or folklore.
William is the third-tier Persona of Ryuji Sakamoto. William specializes in Physical and Electric attacks, allowing him to follow up strikes targeting an enemy's weakness with punishing Physical attacks, especially if Charge is used prior. His Trait is Eccentric Temper, which allows the chance for the allies' physical attacks to increase by 80%.