From Wikipedia (check this link for the references):Pekka Juhana Myrberg (30 December 1892, Viipuri - 8 November 1976, Helsinki) was a Finnish mathematician known for developing
the concept of period-doubling in a paper published in the 1950s.
The concept was further developed by Mitchell Feigenbaum during the 1970s.
Myrberg received his PhD in 1916 at the University of Helsinki under Ernst Lindelöf with thesis Zur Theorie der Konvergenz der
Poincaré'schen Reihen. He began his career by teaching at a Gymnasium, and then became in 1921 professor extraordinarius
and in 1926 professor ordinarius at the University of Helsinki. In 1952 he became the rector and from 1952 to 1962 the
chancellor of the University of Helsinki. In 1962 he retired as professor emeritus but continued publishing
mathematical papers into the 1970s.
In the 1950s Myberg published several fundamental papers on the iteration of rational functions (especially
quadratic functions). His research revived interest in the results of Gaston Julia and Pierre Fatou published during
the beginning of the 20th century.
Myberg was a member of the Finnish Academy of Sciences. In 1954 he was an invited speaker (Über die Integration
der Poissonschen Gleichung auf Riemannschen Flächen) at the International Mathematical Congress in Amsterdam.