1. Shield Sheafson appears in the prologue of Beowulf. He was a king of the Danes, and had recently died; the beginning of the story is his funeral. His name is also translated as Scyld Scefing, Skjoldr, and others.
2. The Danes loved him;
he they carried to the sea's surf, his dear comrades, as he himself had bid, when he yet wielded words, that friend of the Scyldings, beloved ruler of the land, had ruled for a long time; there at the harbour stood with a ringed-prow, icy and keen to sail, a hero's vessel; they then laid down the beloved prince,
He was buried in the manner he had requested, and twice he is called "beloved".
3. His son was named Beowulf (or Beow), but this is not the same Beowulf as the titular character (Beowulf of the Geats, who names his father as Ectheow). Beowulf the Scyld had a son named Half-Dane. Half-Dane had four children; his sons Heorogar, Hrothgar, and Halga, and one daughter, Yrsa. Hrothgar is the aged king of the Danes to which Beowulf of the Geats offers his aid.
Here is a video about the charaters of Beowulf, started at the section pertaining to Shield Sheafson for your convenience:
In a warrior society, a tribal chief or king must exhibit all the attributes prized in a society that is at war on a constant basis. Appropriately, Beowulf begins with just such a king, Scyld Sheaf-Child, whom the Danes view as the ideal warrior-king:
Often Scyld Sheaf-child [or Sheaf-son] scattered his enemies,/captured their mead-halls and cowed their leaders/ . . . /that all those peoples around his borders/over the whale-road [the ocean] had to obey him. . . Now that is a good king!
The Beowulf poet accomplishes two important goals by beginning the poem with this description of Scyld: 1) he provides the model of a great warrior king in Scandinavian and Anglo-Saxon societies and 2) as we learn a few lines later, Scyld founds the dynasty that begins with his son Beow (sometimes call the "other Beowulf"), who then fathers Halfdane, who in turn fathers three sons and one daughter--Heorogar, Halga the Good, Hrothgar, and Yrsa (or Ursa).
As we see when Beowulf introduces himself to Hrothgar as Ecgtheow's son, in this society, one's lineage is all important. Family history and, more important, family honor and courage become the initial measure of a warrior who has yet to prove himself. In both Scandinavian and Anglo-Saxon societies, if one's family has a dishonorable history, all descendants of that family are, at first, assumed to be dishonorable. In the case of Scyld Sheaf-child and his descendants, however, any descendant of a "good king," such as Hrothgar, is presumed to be a good warrior-king.
In sum, then, the opening lines describe both a model warrior-king and explain that Hrothgar, who will be a key figure in the first half of the poem, is a descendant of that "good king" and can therefore be expected to be like his ancestor.