FNU LNU (no relation to GNU)

The Supreme Court just agreed to hear a case captioned,

TANZIN, FNU, ET AL. V. TANVIR, MUHAMMED, ET AL.

Fnu—what kind of a name is that? Danish? Afrikaner?

[Source: Prof. Lisa Davidson, The Atoms of Phonological Representation.]

No, just "First Name Unknown"; likely old hat to many of you, but I didn't learn about it until eight years ago, when I saw United States v. FNU LNU (2d Cir. 2011). It's a federal thing, by the way: A Westlaw search for na(fnu lnu) finds 2516 federal cases (99% since 1994) and only 41 state cases.