He is said to have "bit another passenger" before being restrained.
The Irish news reported the man was "struck down with a seizure" forcing the flight, which departed from Lisbon, to make an emergency medical landing at Cork Airport.
The passenger - who was not believed to be Irish - was reported to have become unwell during the flight, before falling unconscious.
He was declared deceased after failed CPR attempts by paramedics at the airport.
A second man was treated for the bite injury he received while trying to help the ill passenger.
There were 168 passengers and six crew members onboard the Aer Lingus flight, they have since been interviewed by Irish police (gardia) at Cork Airport.
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