Lydia Koidula, Estonian poet and playwright (d. 1886)
Lydia Emilie Florentine Jannsen, (24 December [O.S. 12 December] 1843 – 11 August [O.S. 30 July] 1886), known by her pen name Lydia Koidula, was an Estonian poet. Her sobriquet means 'Lydia of the Dawn' in Estonian. It was given to her by the writer Carl Robert Jakobson. She is also frequently referred to as Koidulaulik – 'Singer of the Dawn'.

In Estonia, like elsewhere in Europe, writing was not considered a suitable career for a respectable young lady in the mid-19th century. Koidula's poetry and her newspaper work for her populist father, Johann Voldemar Jannsen (1819–1890) remained anonymous. In spite of this, she was a major literary figure, the founder of Estonian theatre, and closely allied to Carl Robert Jakobson (1841–1882), the influential radical and Friedrich Reinhold Kreutzwald (1803–1882), writer of the Estonian national epic, Kalevipoeg (The Son of Kalev).