Whether or not Yasuke, an African man who briefly served feudal lord Oda Nobunaga in 16th-century Japan, was "really a samurai" is a somewhat interesting question for scholars of the era, and comes down to how the historical records of his life pair with use of the term "samurai" at the time. Biographer Thomas Lockley, as one example, has said that Yasuke was indeed one of Nobunaga's many samurai, the title simply referring to warriors who served a lord (see: this Smithsonian article).
When Yasuke was revealed as one of the two protagonists in the upcoming Assassin's Creed Shadows, however, an inquisition into his samurai-ness was launched not by scholars, but by onlookers who decreed it unacceptable for a Black person to headline a work of historical fiction set in Japan. Complaints about "historical inaccuracy" and "forced diversity" abounded.
