Georg Ludwig Detlef Theodor Harms (baptised as Ludwig, but called Louis during his life) (1808–1865) was a German Lutheran pastor who was nicknamed the "Reviver of the Heath" (Erwecker der Heide). One of the most significant Christian revivalists of the 19th century, he turned the little village of Hermannsburg on the Lüneburg Heath into the most important centre of revival in Lower Saxony.
Louis Harms was born on 5 May 1808 in Walsrode in north Germany as the second son of a pastor, Hartwig Christian Harms. His mother was Lucie Dorothee Friederike Harms, née Heinze. In 1817 the family moved to Hermannsburg and, in 1825, Louis Harms went to the secondary school in Celle. After passing his A-levels in Celle, Harms studied Protestant theology in Göttingen from 1827 to 1830. His study forced him to confront the Enlightenment, the leading intellectual movement of his time. When he read the verse John 17:3 "Now this is eternal life: that they might know you, the only true God, and Jesus Christ, whom you have sent" he came in 1830 to the conclusion that "it is not enough, just to be religious and good, to live sensibly and act properly, but that it is essential to have Jesus Christ at the centre of one's life and to testify to that."
After passing his exam with honours, Louis Harms worked from 1830 to 1840 as a private tutor for the Lord Chamberlain of Linstow in Lauenburg/Elbe. During this time he held Bible studies and, in 1834, and founded the Lauenburg Mission Society.
After Harms had passed two other theological examinations, but still had no prospect of becoming a pastor, he helped his father in Hermannsburg. Then he returned to being a private tutor in 1840 for the family of state architect, Pampel, in Lüneburg. In Lauenburg and Lüneburg he came across slums, moral neglect and children whose lives were a misery. As a result, visits to the poor, the sick and prisoners became a natural consequence of his faith, an approach that was by no means common at that time.
To support his sick father, at the end of 1843, he returned to Hermannsburg. Harms was appointed as curate to relieve his father and was ordained to the ministry on 20 November 1844. In 1846, he managed to turn the parish of Hermannsburg from a "benevolent society" of the Celle Missionary Society into a "mission parish". Through his church services, parlour gatherings in the rectory, home visits and counselling, a revival started in Hermannsburg. At the request of the municipality, Louis Harms was appointed by the Consistory in Hanover for the Evangelical Lutheran State Church of Hanover as the pastor at Hermannsburg after the death of his father in 1849.