Christian Saints

St. Bartholomew is one of the Apostles of Christ (Mark 3:14-19). After Christ’s death he evangelized Arabia and Mesopotamia, traveled and preached the gospel as far as India, and was martyred in Armenia. It is believed that he was first flayed alive and then crucified on a cross upside down. St. Bartholomew is the patron saint of all trades that deal with skin. In art he is often depicted flayed, carrying his skin, or on a cross turned upside down to make it easier for his torturers to strip off his skin.
See: Agnolo Bronzino. St Bartholomew.
El Greco. St. Bartholomew.
Michelangelo The Last Judgment   St. Bartholomew is on the right of the God, holding his skin.
Jusepe de Ribera. The Martyrdom of St. Bartholomew.
Konrad Witz St. Bartholomew.

Recommended reading:
The Book of Saints: The Lives of the Saints According to the Liturgical Calendar by George Angelini, Victor Hoagland (Editor). Regina Press, Malhame & Company, 1986.