(29 December 1815, Copenhagen - 28 Januar 1882, Rome) was a Danish artist who specialized in genre painting.
Following an apprenticeship with J.G. Berg in Copenhagen, Hammer was admitted to the Danish Academy in 1828. In 1841, he became a student of Christoffer Wilhelm Eckersberg who remained a close friend. He was awarded the Academy's little silver medal in 1842 and the large silver medal the following year. Det sidste Læs, his entry for the Neuhausen Prize in 1845, was bought by Statens Museum for Kunst but it was not until 1837 that he was awarded the prize with Bønder forsamlede til Lystighed en Søndag Eftermiddag under aaben Himmel.
Hammer was an industrious but rather serious and thoughtful artist. His avid approach to detail slowed down his work considerably. After the outbreak of war in 1848, he became a naval officer. With a stipendium from the Academy, he travelled to Italy in 1857 where he painted Torvet i Ariccia efter Solnedgang, considerably enhancing his reputation in Denmark. The painting was acquired by Statens Museum for Kunst in 1863. Other notable works are Axsamlersken (1866) and Postbudet med det længe ventede Brev (1877). After recovering from a serious illness, he travelled to Rome in 1881 but died there the following year