Diomedes Díaz Maestre (26 May 1957 – 22 December 2013) was a Colombian vallenato singer, songwriter, and composer. He has been named the "King of Vallenato" and is nicknamed El Cacique de La Junta (The Chieftain of La Junta), which was given to him by another vallenato singer, Rafael Orozco Maestre, in honor of Díaz's birthplace.

Diomedes Díaz is the biggest record seller in the history of vallenato, exceeding 10 million throughout his career, due to this, he was awarded gold, platinum and diamond records, unique in Colombia until 2008. In 2010 he won the Latin Grammy in the "Cumbia / Vallenato category". Loved and idolized by many, Diomedes' followers adopted the nickname "diomedistas", while Diomedes called them his "fanaticada".

His personal life was marked by family instability, controversial friendships, ups and downs with the consumption of alcohol and drugs, accidents, financial and legal problems, especially the death under strange circumstances of Doris Adriana Niño.