True Potterheads know that the magical world has never been short on tragic drama or the portrayal of greyness between good and evil. In The Crimes of Grindelwald, there's a mysterious wizard who embodies both so deeply, someone who acts by his own set of rules and motivations as Grindelwald's rise calls for people to choose sides. Enter Yusuf Kama (William Nadylam). At first glance, he appears to be a French Auror or Ministry employee tracking down Credence Barebone (Ezra Miller). But, of course, he has painfully personal stakes in finding the powerful Obscurial. For the prequel lore-obsessed, here's a brief rundown on Yusuf's thorny past and his relationship to the Lestrange family.
We first meet the French-African wizard when he spots Tina at a circus and tells her that he too is looking for Credence. But his intentions aren't so noble in reaching out to her, and he locks her up in his creepy makeshift sewer hideout. When he brings Newt down to the dungeon-like area, the magizoologist frees the Auror and keeps Yusuf at Nicolas Flamel's after knocking him out. But being resourceful, Yusuf escapes when Jacob isn't looking. Eventually, however, he finds himself with Leta, Newt, Tina, Nagini, and Credence all at once.
Here's the skinny on why Yusuf has been hunting Credence. Yusuf is actually the half-brother of Newt's friend Leta Lestrange (Zoë Kravitz). Many years ago, Corvus Lestrange IV had used the Imperius Curse on Yusuf's mother, which, with very dark implications indeed, leads to Leta's conception. Their mother dies in childbirth, and the nefarious Lestrange would go on to have another son, Corvus Lestrange V. At his father's deathbed, Yusuf makes an Unbreakable Vow to kill the person that the senior Lestrange cares for the most, aka his son Corvus V. For a long time, he believed that Credence Barebone, who had been put up for adoption by the Lestrange's housekeeper, was actually Corvus V.
But there's a plot twist. Leta reveals to Yusuf that Credence, in fact, is not her brother. When she was much younger, her real brother had been crying uncontrollably while they were boarding a ship to America together, so she switched him with another baby. When their boat sank, the lifeboat with her brother on it flipped over, so Corvus V drowned to death.
Besides his tragic family backstory and bloodthirsty hunt for Credence, there's not much that we know about Yusuf, other than that he claims to be the last male in his pure-blood family line. Still, we wouldn't be surprised if his story expands in the next Fantastic Beasts installation, as we last see him walking with the Aurors to Dumbledore.