Ongentheow was the name of a semi-legendary Swedish king of the house of Scylfings, who appears in Old English sources.

The Ynglings were a dynasty of kings, first in Sweden and later in Norway, primarily attested through the poem Ynglingatal. The dynasty also appears as Scylfings in Beowulf. When Beowulf and Ynglingatal were composed sometime in the eighth to tenth centuries, the respective scop and skald (poet) expected his audience to have a great deal of background information about these kings, which is shown in the allusiveness of the references.