Feynman's first wife, previously his local-high school darling.
Feynman was like an reversed Stephen Hawking: he married his wife knowing that she had a serious illness, while Hawking's wife married him knowing that as well.
Just that in Feynman's case, the disease outcome (tuberculosis) was much more uncertain, and she tragically died in 1945 much earlier while Feynman was at Los Alamos Laboratory, while Hawking, despite his decline, lived much longer.
Reading about her death e.g. at Genius: Richard Feynman and Modern Physics by James Gleick (1994) is a major tearjerker, it's just too horrible. The book mentions on chapter "The Last Springtime" that at last, during the last months of her life, after much hesitation, they did fuck in the sanatorium Arline was staying at in Albuquerque, the nearest major city to Los Alamos, despite the risk of Feynman being being infected, which would be particularly serious given that Feynman would be in constant contact with students and possibly infect others as part of his career as a researcher/teacher.
It is even sadder to think that the first antibiotics for tuberculosis, streptomycin, finished its first major clinical trial at around 1948, not long after her death.
Ciro Santilli considers this tragedy a cause of Feynman was a huge womanizer during a certain period of his life.