The first appearance of Hroar (Hrothgar) in literature is in Widsith and Beowulf, where we become acquainted with him as the famous King of the Danes. Helgi (Halga) appears first in Beowulf, where he is scarcely more than mentioned. Hroar and Helgi belong to the most famous group of ancient kings in Denmark and appear repeatedly in old Scandinavian literature. The account of them in the Fróðaþáttr which introduces the Hrólfssaga, is, briefly summarized, as follows.
Halfdan and Frothi were brothers, the sons of a king, and each was the ruler of a kingdom. Halfdan had two sons, Hroar and Helgi, and a daughter, Signy, the oldest of the three children, who was married to Earl Sævil while her brothers were still young. The boys' foster-father was Regin. Near Halfdan's capital was a wooded island, on which lived an old man, Vifil, a friend of Halfdan. Vifil had two dogs, called Hopp and Ho, and was skilled in soothsaying.
Frothi, envying his brother the crown of Denmark, attacked his capital with a large army, reduced it to ashes, and took Halfdan captive and put him to death. Regin took his foster-sons, Hroar and Helgi, to the island and placed them in the care of Vifil, in order that they might not fall into the hands of Frothi. Vifil took them to a cave (earth-hut), where they usually stayed at night; but in the daytime they sported in the grove. Frothi made every effort to locate them and make away with them, calling in witches and wise men from all over the land to tell him where they were, but in vain. Then he called in soothsayers, who told him the boys were not on the mainland, nor far from the court. The king mentioned Vifil's island, and they told him to look for the boys there. Twice he sent men to search for them, but the men failed to find them. Then the king went himself. Vifil, who knew the king was coming, met him on the strand as if by chance, pretending to be looking after his sheep; and when the king bade his men seize Vifil, the old man said, "Do not detain me, or the wolves will destroy my sheep," and cried out, "Hopp and Ho, guard my sheep." The king asked him to whom he was calling; he said, to his dogs. But he had told the boys before, that, when he called out the names of his dogs, they should hide in the cave. The king failed to find the boys and returned; but Vifil told the boys that it was not safe for them to remain on the island and sent them to their brother-in-law, Sævil, saying that they would some day be famous, unless, perchance, something prevented it.
Hroar was now twelve years old and Helgi ten. The boys returned to Sævil, but, calling themselves Hrani and Hamur, did not tell him who they were; and as they always wore masks, their identity remained unknown to him.
Frothi invited Sævil to a feast. Hroar and Helgi expressed a wish to join him; but Sævil commanded them to remain at home. Nevertheless, when Sævil and his retinue had started off, Helgi got an untamed colt, and mounting it with his face toward the horse's tail, set out, acting all the while very foolishly. Hroar also mounted a colt, and joined him; and the two overtook the company. They galloped back and forth beside Sævil's retinue, until finally Helgi's mask fell off, and then Signy recognized him. She began to weep, and when Sævil asked her the cause of her distress, she informed him of her discovery. Sævil tried to get the boys to return home; but, though they now were on foot and remained in the rear, they persisted in accompanying him on his visit to Frothi.
When they arrived at Frothi's, Frothi began to hunt for the boys, and bade a witch, who had come to the hall, to try her skill in finding them. She told him that they were in the hall. Then Signy threw her a gold ring, and the witch said that what she had just stated was false. Frothi threatened to torture her if she did not tell the truth; and she said that unless he soon prevented it, which he would not do, the boys would be his death. But the boys, terrified, fled to the wood. The king ordered his men to seize them; but Regin put out the lights in the hall, and, in the confusion that followed, those who were friendly to the boys used the opportunity to obstruct those who would pursue them. Frothi vowed that he would take vengeance at a more suitable time on those who had assisted the boys, but added, "Let us now drink and feast"; and this they did till the men lay in a drunken stupor in a heap on the floor.
Regin rode out to where the boy's were, but would not return their salutation. In fact, he pretended to be angry. They wondered what this meant, and followed him. Helgi thought that Regin wanted to help them, but without violating his oath to the king. Then Regin said to himself, so that the boys heard it, "If I had a matter to settle with the king, I would burn this grove." They took the hint and started a fire. Sævil came out with all his men and bade them aid the boys, and Regin took measures to get all his men and relatives out of the hall. The king awoke from a dream, in which the goddess of the nether world was summoning him. He discovered the fire, and learning who had set it, offered the boys peace on their own terms; but terms of peace were denied. Frothi then retired from the door of the hall, hoping to escape by an underground passage; but at the entrance stood Regin, who blocked his progress, and he returned into the hall and perished in the flames. His wife, Sigrith (now mentioned for the first time), the mother of Hroar and Helgi, refused to leave the hall and perished also.
The boys thanked their brother-in-law, Sævil, and their foster-father, Regin, and all the others who had helped them, and gave the men rich gifts. The boys subdued the whole land and seized the late king's possessions; and for a while the time passed without the occurrence of anything worthy of special mention.
At this time there was a king by the name of Northri, who ruled over a part of England. Hroar often passed long intervals at the court of Northri, supporting him against his enemies and defending his land. Hroar married Ögn, the daughter of Northri, shared the royal power with his father-in-law, and after Northri's death succeeded to the throne of Northumberland. Helgi remained at home, and, by agreement with Hroar, became sole King of Denmark.
In Saxo's seventh book, there is another version of the same story. The features in which it chiefly varies from the version in the Hrólfssaga are as follows.