“Loki begat the wolf
With Angrboda,
And Sleipnir
With Svadilföri;
One monster was thought
Most terrible of all;
It was sprung from
The brother of Býleist (= Loki).”
[Hyndluljód, 40]
The Asar were afraid of Fenrir wolf, Loki’s son, and twice tried to chain it, but could not.