Tanja Mirjam Cecilia Lorentzon (née Tanja Mirjam Cecilia Koukonen; born 25 September 1971), previously known as Tanja Svedjeström, is a Sweden-Finnish actress and dramatist of Finnish descent. Internationally, she is probably best known for her role of Sonja Modig in The Girl Who Played with Fire and The Girl Who Kicked the Hornets' Nest, film adaptations of the Millennium series by Stieg Larsson.

Lorentzon was born in Tumba, Stockholm County, Sweden, to Finnish parents. In her youth, Lorentzon worked as an engineer in the Ericsson, Inc., a cleaner and a teacher before entering the Swedish National Academy of Mime and Acting in 1994. She earned her bachelor's degree in 1998.

Lorentzon currently lives in Stockholm with her husband and their three daughters.^[1]

In 2010, Lorentzon debuted as a screenwriter with her monologue play Grandmother's Dark Eyes (Swedish: Mormors mörka ögon), in which she played all three characters — herself, her mother and her grandmother. The plays follows lives of . In December 2010, Grandmother's Dark Eyes was broadcast on the STV.^[1] The following year, Lorentzon was awarded with the P7 Sisuradio Award for Swedish Finn of the Year for her work on Grandmother's Dark Eyes.^[2]