Joker, the protagonist of Persona 5, was released as Ultimate's first Fighters Pass character.
Nintendo revealed Joker at The Game Awards in December 2018, shortly after Ultimate's launch. He became the first paid downloadable fighter in the original Fighters Pass and arrived in April 2019, accompanied by the Mementos stage and music from the Persona series.
In battle, Joker fights with a knife and gun and can summon Arsène, a powerful Persona that enhances several of his attacks. His inclusion was notable because Persona 5 had not originally been released on a Nintendo platform, making him one of Ultimate's prominent third-party additions.
The other choices belong to later points in the DLC lineup. Hero was the second Fighters Pass fighter, Terry Bogard was fourth, and Byleth was fifth. Piranha Plant was released before Joker but was separate from the Fighters Pass, so it is not the answer to this wording.