Theobald Reinhold Freiherr von Oer (9 October 1807 – 1885 in Coswig) was a German painter, illustrator and etcher.
Theobald von Oer, born at Haus Nottbeck, Stromberg, was the son of a Westphalian district administrator.
At the age of 12, he fell ill with scarlet fever and lost his hearing as well as parts of his speech.
He proved himself exceptionally talented and quickly changed to further studies to the Kunstakademie Düsseldorf, under the teaching of W. von Schadow.
In 1836, he and architect H. Matthäi travelled together through the Netherlands and Belgium, eventually arriving at Paris, visiting various French artists.