From Halopedia, the Halo wiki
The father of Bornstellar Makes Eternal Lasting was a powerful Forerunner Builder. He and his guild designed the original twelve Halo rings under the orders of the Master Builder, Faber. He was married to another Builder with whom he had several children, including Bornstellar and his sister.
Though he had many children, Bornstellar was the most rebellious of them all, refusing to undergo the intensive training and education expected of him. Bornstellar's rebellion eventually led his father to send him to a step-family of Miners on Edom, where his father hoped he would learn discipline. Eventually, however, Bornstellar escaped to Erde-Tyrene and ended up reviving the Didact and joined the Promethean on a mission across the galaxy, until he was caught by the Master Builder and sent back to his family. Some time after Bornstellar's return, his father met with another high-ranking Builder and learned that the Master Builder had used a Halo against the San'Shyuum and would be tried for violation against the Mantle as a result. This would also result in him and his guild being indicted for designing the Halo weapon.
The next morning, Bornstellar confronted his family, bearing a message from the Didact's imprint within, concerning the Halo tested at Charum Hakkor. Bornstellar's father was hesitant to discuss the Halos openly at first, but eventually realized this was futile and revealed that Bornstellar's presence was requested at the Master Builder's trial. Before Bornstellar departed for the Capital, he met with his father who, despite being saddened to see his son taken from his family, told him that he placed all his hope in his son. Bornstellar never saw his father or the rest of his family again—"alive and free".
Bornstellar's father was over six thousand years old by the mid-97,000s BCE. He had undergone a further mutation during Bornstellar's absence and stood over four meters tall, as was typical of Forerunners of his rank. Bornstellar noted that his father's newest form bore a disturbing resemblance to the Master Builder, who the Manipular had recently crossed paths with.
List of appearances