Hella Maria Wuolijoki (née Ella Maria Murrik; 22 July 1886 – 2 February 1954), known by the pen name Juhani Tervapää, was an Estonian-born Finnish writer, playwright, parliamentarian, businessperson and farmer. She is best known as a dramatist, particularly for the Niskavuori series of plays and for her collaboration with Bertolt Brecht on Mr Puntila and his Man Matti. Wuolijoki served as the Director General of Yle from April 1945 to June 1949 and was a member of the Parliament of Finland from 1946 to 1948. She also played a private role in the peace negotiations during the Winter War through her friendship with Alexandra Kollontai.

Ella Murrik was born on 22 July 1886 in Ala, Governorate of Livonia (present-day Estonia) to Ernst Murrik and Katarina Kokamägi. One of five siblings, Wuolijoki was the elder sister of Salme Pekkala-Dutt, a member of the Communist Party of Great Britain.

Wuolijoki attended school in Tartu. In 1904, Wuolijoki moved to Helsinki to study folklore, history and Russian at the Imperial Alexander University. During this period Wuolijoki participated in the 1905 general strike. Wuolijoki graduated in 1908, making her the first Estonian woman to graduate from the university with a Master's degree. Wuolijoki began a PhD in Estonian folklore under the supervision of Kaarle Krohn, but did not complete her studies.

Wuolijoki initially worked as a journalist and by giving private Russian language lessons. In April 1906, Wuolijoki was one of two female journalists to cover the first State Duma.

In the 1910s Wuolijoki began working as a secretary for an international trade agent before being an agent herself. The outbreak of the First World War opened a wide field for her organisational skills: public and private property was transferred between countries on paper and partly in practice through her mediation, earning her substantial commission fees. Wuolijoki later operated her own trading firm, and traded primarily in sugar, coffee, wheat and timber from South America, Sweden and the United States. During the early years of the Russian Revolution Wuolijoki was the only Western woman trade agent operating in present-day Russia. Her trading activities extended from sawmill companies in eastern Finland to English firms with an emphasis on the timber trade, but these ventures collapsed during the Great Depression.

Among Wuolijoki's new acquaintances during the war years was Harold Granville Grenfell, the British naval attaché in Saint Petersburg and a member of the left wing of the British Labour Party, whose contacts opened connections for Wuolijoki to British politics.

Wuolijoki's first play, Talulapsed, was published in 1912 and staged the following spring at the Estonia Theatre in Reval (Tallinn), but was banned immediately after its premiere on political grounds for being too nationalist; the Finnish-language version Talon lapset met the same fate at Kansan näyttämö two years later. Her novel Udutagused (1914) has been regarded as her principal Estonian-language work, and her poetic work Sõja laul (1915), based on Jakob Hurt's collection of folk poetry, later became known internationally as a fragment incorporated into Bertolt Brecht's The Caucasian Chalk Circle.

From the 1930s onwards, Wuolijoki's themes and settings were located in Finland. In 1933, the Ministry of Justice banned her play Laki ja järjestys (Law and Order) after its first performance; the play dealt with the Finnish Civil War and showed sympathy for both sides, and press debate about it cemented perceptions of Wuolijoki's left-wing sympathies.