David Kimchi (known as RaDAK) was born in 1160. Both his father, Joseph Kimchi (known as the RIKaM), and his brother, Moses ben Kimchi (known as the ReMaK) were great grammarians. They joined the controversy between Jonah ibn Yanach and David Hayyuj about the nature of Hebrew grammar.
David Kimchi was able to present their positions clearly and simply in a user- friendly format, his grammar/lexicon Michlol. In it, RaDaK presented the idea that there were long and short vowels (anyone who has studied Hebrew grammar is now saying, "Ah He's the one who's guilty..."). He defined the nif'al as the passive of the kal.
RADaK wrote biblical commentaries in which he attacked Christian misunderstandings of text (a gutsy thing to do).
David Kimchi is best known, however, for his defense of Maimonides' Guide For the Perplexed during the second Maimonidean Controversy.
When Solomon ben Abraham of Montpellier arranged to have the Guide For the Perplexed banned, RaDaK wrote angry letters against the ban. When he heard that Judah ibn Alfakhar was against permitting the Guide, Kimchi set up a correspondence with him, trying to convince him that the Guide was not a dangerous book. He died before he was able to reach Toledo to meet with Judah ibn Alfakhar in person.
Sources: Gates to Jewish Heritage