Carlos Ibáñez e Ibáñez de Ibero, 1st Marquis of Mulhacén, (April 14, 1825 - January 28 or 29, 1891) was a Spanish divisional general and geographer.
He represented Spain at the 1875 Conference of the Metre Convention and was the first president of the International Committee for Weights and Measures.
As a forerunner geodesist and president of the International Geodetic Association, he played a leading role in the worldwide dissemination of the metric system.
His activities resulted in the distribution of a platinum and iridium prototype of the metre to all States parties to the Metre Convention during the first meeting of the General Conference on Weights and Measures in 1889.
These prototypes defined the metre right up until 1960.He was born in Barcelona.
According to Spanish tradition, his surname was a combination of his father's first surname, Martín Ibáñez y de Prado and of his mother's first surname, Carmen Ibáñez de Ibero y González del Río.
As his parent's surnames were so similar he was often referred as Ibáñez or Ibáñez de Ibero or as Marquis of Mulhacén.
When he died in Nice (France), he was still enrolled in the Engineer Corps of the Spanish Army.
As he died around midnight, the date of his death is ambiguous, Spaniards retained 28th, and continental Europeans 29 January.