Dravidian is a family of about twenty six languages, principally Tamil, Telugu, Kannada and Malayalam in southern India, with Tulu, Kodava and a group of smaller languages in central India, and Brahui, spoken in Balochistan a long way from the rest. Bhadriraju Krishnamurti's comparative grammar is the standard modern account. The family is not related to Indo-Aryan, and the two have been in contact long enough to have reshaped one another.
That contact is itself a religious fact. Sanskrit acquired retroflex consonants, which Dravidian has and which Indo-European elsewhere does not, and the Dravidian languages took in enormous Sanskrit vocabulary for religious and philosophical concepts. The Indus valley script is undeciphered, and a Dravidian reading of it is one of the leading proposals and remains unproven; the atlas records that question as open.
Tamil has the oldest literature of the family and the oldest surviving in any Indian language other than Sanskrit, with the Sangam poems and then the Shaiva and Vaishnava hymns that gave bhakti its first vernacular canon. Telugu, Kannada and Malayalam each developed their own devotional literatures, and Kannada in particular produced the Virashaiva vachanas, short prose poems attacking temple religion and caste.