What is Grendel's lineage that is given in the first stanza What allusion is used to describe these monsters?

In the first stanza of "Beowulf," Grendel's lineage is described as being descended from Cain, the biblical character who committed the first murder by slaying his brother Abel. This allusion to Cain serves to position Grendel and his mother as outcasts and evil beings, mirroring the biblical narrative of Cain's exile and curse.