Jacob Ludwig Karl Grimm (4 January 1785 – 20 September 1863), also known as Ludwig Karl, was a German author, linguist, philologist, jurist, and folklorist. He formulated Grimm's law of linguistics and was the co-author of the Deutsches Wörterbuch, the author of Deutsche Mythologie, and the editor of Grimms' Fairy Tales. He was the older brother of Wilhelm Grimm, and together, they were known as the literary duo, the Brothers Grimm.

In 1822, Jacob Grimm formulated Grimm's Law, the basis for much of modern comparative linguistics. This law describes the regular sound changes that Indo-European stop consonants underwent in Germanic languages. For instance, Indo-European 'p' shifted to Germanic 'f', 't' to 'th', and 'k' to 'h'. Indo-European 'b' shifted to Germanic 'p', 'd' to 't', and 'g' to 'k'. Indo-European 'bh' shifted to Germanic 'b', 'dh' to 'd', and 'gh' to 'g'.

Beyond his linguistic contributions, Jacob Grimm was a jurist and mythologist, and he also authored the monumental German Dictionary.