During the Vietnam war, Grothendieck taught math to the Hanoi University mathematics department staff, out in the countryside. Hoàng Xuân Sính took notes and later did a PhD with him - by correspondence! She mailed him her hand-written thesis.
First, some background. Hoàng Xuân Sính was born in 1933, one of seven children of fabric merchant. She got her PhD in 1975, and later became the first female math professor in Vietnam. In 1988 she started the first private university in Vietnam.
Her thesis classified Gr-categories, which are now called '2-groups' for short. A 2-group is the categorified version of a group: it's a monoidal category where every object and morphism is invertible.
(An object X is invertible if there's Y with X⊗Y ≅ Y⊗X ≅ I.)