Worshiping San Fermín in Pamplona took place long before the Sanfermines, and his image is still the focus around which this universal "fiesta" revolves.  According to tradition, a presbyter called Honesto arrived in Roman Pamplona in the 3rd century. He had been sent by San Saturnino (also known as San Cernín) to evangelise the city and he converted senator Firmo and his family to the Christian faith. His son Fermín was christened by San Saturnino at the place now known as the Pocico de San Cernin(little well of San Cernín) and was ordained into the priesthood in Toulouse (France). He returned to Pamplona as Bishop and died, decapitated, in Amiens, where he baptised more than 3,000 people.

San Fermín was the 1st Bishop of Pamplona, although his veneration is not recorded until the 12th century thanks to litanies from Amiens, in which he appeared from the 8th century onwards. San Fermín is now co-patron saint of Navarre with St Francis Xavier, and is also the patron of boot makers, wine traders and bakers.