Oddr Snorrason

The Óláfs saga Tryggvasonar of Oddr Snorrason whose name is also sometimes Anglicized as Odd Snorrason was a Latin royal biography attributed to a 12th-century Icelandic Benedictine monk at the Þingeyrar monastery (Þingeyrarklaustur). The monastery was founded in 1133 and was the first in Iceland.
Its subject is the 10th-century Norwegian king Óláfr Tryggvason. The original work has been almost completely lost but a translation into Old Norse is preserved in two nearly complete versions and a fragment of a third. The work is often referred to as Óláfs saga Tryggvasonar. Oddr made use of previous written works including those of Sæmundr fróði and Ari Þorgilsson as well as Acta sanctorum in Selio and possibly Historia de Antiquitate Regum Norwagiensium. In turn Snorri Sturluson made use of Oddr's work when writing the Heimskringla, as did the author of Óláfs saga Tryggvasonar en mesta.
It is difficult to tell how closely the Old Norse translation of Oddr's Óláfs saga resembles the Latin original but it clearly owes a debt to hagiography, presenting King Óláfr as the apostle to the Norwegians.
Yngvars saga víðförla also credits Oddr with its original authorship. Scholars have been skeptical towards this claim but in recent years it has gained more acceptance.