1610, "a person in despair," mock-Spanish version of
desperate (n.) "reckless criminal" (1563), from L.
desperatus (see
desperation). There was an adj.
desperado in O.Sp., meaning "out of hope, desperate," but apparently it never was used as a noun and it probably has nothing to do with the Eng. word. Meaning "a desperate or reckless man" is recorded from 1647.