Vaithamanithi Mudumbai Kothainayaki Ammal (1 December 1901 – 20 February 1960), familiarly known as Vai Mu Ko, was a Tamil writer, novelist, and journalist who was the first woman to occupy the editorial board of a Tamil magazine.
She wrote 115 books and published a monthly Tamil magazine, Jaganmohini.
Kothainayaki was the first female writer in Tamil to write a detective novel.
She was interested in a variety of topics and excelled in fields like public speaking, social service, music composition, and fiction writing.
Kothainayaki was also a feminist and a freedom fighter.
She was hailed as the "Queen of Fictions" by contemporary authors.
However, Kothainayaki was not well recognized in books about the history of Tamil literature.