Cosmas and Damian (unfortunately reproduced in many hoodoo-type places as Comas or Cosmos and Damien) were twin brothers and physicians who lived in Asia Minor in the 3rd century. They got martyred during the reign of Diocletian. Diocletian, an autocrat and anti-republican who eventually took the name Dominus et Deus (Lord and God), made a lot of martyrs. He ordered the greatest persecution of Christians in the Roman Empire that the Empire had yet seen. (This is the sweep that got St. Sebastian, one of my dear personal saints).
Cosmas and Damian are, predictably, called on for cases of illness, and as the patron saints of doctors and pharmacists.
In voodoo, they are often associated with the loa the Marassa ("Twins").
Prayer for communion, ref Ps. 78, 2. 11. "They have given the dead bodies of Thy servants to be meat for the fowls of the air: the flesh of Thy Saints for the beasts of the earth: according to the greatness of Thy arm, take possession of the children of those who have been put to death."