Saint Fermin is one of many locally venerated Catholic saints. Fermin is the co-patron of Pamplona, where his feast, the 'San Fermin', is forever associated with the Encierro or 'Running of the Bulls' made famous by Ernest Hemingway.

Fermin is said to have been the son of a Roman of senatorial rank in Pamplona in the 3rd century, who was converted to Christianity. According to tradition, he was baptised by Saint Saturnin at the spot now known as the Pocico de San Cernin, the "Small Well of San Cernin," across from the facade of the church dedicated to St Cernin, which is built on the foundations of a pagan temple. Saturninus, Sernin or Cernin, was the first bishop of Toulouse, where he was sent during the "consulate of Decius and Gratus" (250 AD). He was martyred (traditionally in 257 AD), significantly, by being tied to a bull by his feet and dragged to his death, a martyrdom that is sometimes transferred to Fermin and relocated at Pamplona. In Toulouse, the earliest church dedicated to Notre-Dame du Taur ("Our Lady of the Bull") still exists, though rebuilt; though the 11th Century Basilica of Saint Sernin, the largest surviving Romanesque structure in France, has superceded it, the church is said to be built where the bull stopped, but more credibly must in fact be on a site previously dedicated to a pre-Christian sacred bull, perhaps the bull of Mithras. The street, which runs straight from the Capitole, is named, not the rue de Notre-Dame, but the rue du Taur.

Fermin was ordained a priest in Toulouse, according to the local legend, and returned to Pamplona as its first bishop. On a later voyage preaching the gospel, Fermin was beheaded in Amiens, France, on September 25, 303 AD.

Besides Pamplona, San Fermin is venerated in other places in Navarre, such as Lesaka, in the fiesta called the Regata del Bidadosa. In the village of San Fermin de Aldapa, the martyrdom of Saint Fermin is still commemorated on September 25. On the preceding Thursday to Sunday there are numerous festivities there, in the Navarrería and near the Cathedral. Celebrations begin with a firework rocket set off by a youngster from the Navarrería, who has been given the title of the little mayor. As at Pamplona, the celebrations have a special closing ceremony called Pobre de Mí.

There is a mysterious well of an otherwise unknown "Saint Farmin" at Bowes, Yorkshire, England.

• St. Farmin's Well.

When certain relics of the saint were brought back to Pamplona in 1196, the city decided to mark the occasion with an annual event. Over the centuries, the saint's festival, the ancient annual fair and the running of the bulls and subsequent bullfights have all melded together.

For the Running of the Bulls, see Pamplona.