Even if we go back to Viking times, Stavanger was a center for trade and commerce, although it did not get status as a city before 1425. Stavanger is only mentioned once in Snorri Sturluson's sagas - in Arnor Jarleskalds ode to Magnus Olavsson the Good on his way to Denmark in 1042:
The bishopric of St. Svithun, or Stavanger, included remote places like Eidfjord in Hardanger, Røldal, Hallingdal and Valdres together with the counties of Rogaland and Agder.
The building of the church started in 1123 - 1128. The first bishop was a Benedictine monk named Bishop Reginald (or Reinald) from Winchester, England. Stavanger Cathedral is also called St. Svithun Cathedral after a 9th century bishop from Winchester who was canonized.
Since a cathedral of this size cost a lot of money, Reginald was always in lack of money. When King Sigurd - The Crusader (Sigurd Jorsalfar) was denied being married by the bishop in Bergen, due to Sigurd's divorce from Queen Malmfrid, he asked Reginald to marry him to his new queen - Cicilia. Sigurd donated land and money to the bishopric.
After both King Sigurd and his son, Magnus, were dead, King Harald Gille had Bishop Reginald hung in Bergen since he refused to tell them were Magnus' treasures were hidden. Reginald would rather die than let the bishopric in Stavanger lose it's wealth.
The next bishop in Stavanger was bishop John Birgersson who later became Norway's first archbishop.
You can read more about our great cathedral at Wikipedia.
Pulpit Rock - view from Lysefjorden
Reginald, an Englishman and most probably a Benedictine monk from Winchester cathedral, was the first Bishop of Stavanger.