Cassius Tocqueville Ionescu Tulcea (Romanian: Casius Ionescu-Tulcea; October 14, 1923 – March 6, 2021) was a Romanian-American mathematician, specializing in probability theory, statistics and mathematical analysis.
In 1957 he moved to the United States with his wife Alexandra Ionescu Tulcea (née Bagdasar), who had been his student.
He received his doctorate from Yale in 1959 under the supervision of Einar Hille with thesis Semi-groups of Operators.
During their marriage, the two mathematicians wrote a number of papers together, as well as a well-regarded research monograph on lifting theory.
He turned 90 in October 2013[4] and died in Chicago, Illinois, in March 2021, at the age of 97.