Which Viking-age Norwegian king was nicknamed Olaf the Stout?

The Viking-age Norwegian king nicknamed Olaf the Stout was Olaf II of Norway.

Olaf II Haraldsson ruled Norway from 1015 to 1028 and is commonly called Olaf the Stout, or Olaf the Fat, in English translations of his Old Norse byname. He worked to strengthen royal authority and promote Christianity across Norway.

After being driven from the kingdom by Cnut the Great, Olaf returned in 1030 and was killed at the Battle of Stiklestad on 29 July. His supporters soon treated him as a saint, and his cult became central to medieval Norwegian identity. Nidaros, modern Trondheim, developed as an important pilgrimage center associated with his shrine.

Olaf II is often confused with Olaf Tryggvason, another Norwegian king who ruled earlier, from 995 to 1000. The two rulers shared the name Olaf and were both associated with Christianization, but they were different historical figures.