Who was the most powerful Norse god?
Hel (being)
In Norse mythology, Hel is a being who presides over a realm of the same name, where she receives a portion of the dead. Hel is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. In addition, she is mentioned in poems recorded in Heimskringla and Egils saga that date from the 9th and 10th centuries, respectively. An episode in the Latin work Gesta Danorum, written in the 12th century by Saxo Grammaticus, is generally considered to refer to Hel, and Hel may appear on various Migration Period bracteates.
Almáttki áss
The expression could also refer to Odin, as the most important god of the Norse pantheon. But apart from the fact that his cult was not very widespread in Iceland, his unpredictable nature strongly goes against this solution.