Cathleen Synge Morawetz (1923 – 2017) was a Canadian mathematician who spent much of her career in the United States. Morawetz's research was mainly in the study of the partial differential equations governing fluid flow, particularly those of mixed type occurring in transonic flow. She was professor emerita at the Courant Institute of Mathematical Sciences at the New York University, where she had also served as director from 1984 to 1988. She was awarded the National Medal of Science in 1998.
Ever since as a kid I read a story about a beautiful Irish Countess Cathleen, I have loved this spelling of the name. I think Kathleen looks frumpy. Cathleen looks prettier to me, and I'd consider it as a middle name.
When I commented above (or perhaps I should say 'below'), regarding the Countess Cathleen, I had not realized that the legend referred to is the subject of a poem by W.B. Yeats. https://en.wikipedia.org/wiki/The_Countess_Cathleen So Cathleen can be considered a famous literary person. I still prefer that spelling to Kathleen.