Ciro Santilli Feynman's first wife, previously his local-high school-days 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. Except 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.
Feynman first noticed Arline on the beaches on the region of his home in Far Rockaway, in the Queens, New York, near Long Beach. She lived a bit further inland in Cedarhurst. Arline was beautiful and boys competed for her, but Richard persisted, stalking her at an after-school social league sponsored by the local Synagogue and joining an art class she went to, until he eventually won it out. The region was highly Jewish, and both were from Jewish families, as also suggested by their family names.
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 where was staying at in Albuquerque, the nearest major city to Los Alamos (154 km), despite the risk of Feynman 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. Feynman would visit her on weekends by bus, and stay in Los Alamos during the week.
Arline finally died on June 16th 1945, exactly one month before the Trinity nuclear test was carried out. The atomic bombings of Hiroshima and Nagasaki were a little later on 6 and 9 of August 1945.
On one of his last trips to Oak Ridge town late 1945, after her death, Feynman walked past a shop window and saw a pretty dress. He thought to himself, "Arline would have liked that", and the reminder made him cry for the first time after Arline's death.
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.
The film suggests that Feynman and Arline fucked a lot before the final Los Alamos fuck, that fuck story from book being only "fuck after tuberculosis diagnosis", after which they had to slow it down a bit.
This is likely true given how long they had been together for at that point. Ciro Santilli is such a pure soul for not having thought that! They were not very conservative at all those two.
Also their wedding got slowed down because there was a clause in Feynman's scholarship at Princeton University stating that the recipient could not be married, those were different times altogether.