We have no precise dating for the establishment of Belegost, but according to The Grey Annals in volume XI of The History of Middle-earth, the Dwarves of Belegost first became known to the Eldar in Valian Year 1250. Translating to solar years, this means that Belegost existed at least 2,400 years before the Return of the Noldor and the first rising of the Moon and Sun.

We're also lacking any detailed information about the history of the Dwarves of Belegost and their rulers, and indeed it is conceivable that they did not have a lord throughout their entire history. In an account of their work in the making of Menegroth, soon after their appearance in Beleriand, it is perhaps notable that their leader is referred to as the 'chieftain of the Dwarves of Belegost' rather than their lord (Quenta Silmarillion 10, Of the Sindar). This may be no more than insignificant choice of wording, but it may conceivably imply a change in the organisation of the Dwarves over time.

The Dwarves of Belegost did not belong to the Longbeard clan (commonly known as Durin's Folk) who played a large part in the events of the Third Age. Rather, they were descended from another of the Fathers of the Dwarves, and indeed if they followed the pattern of the Longbeards, the Lord of Belegost would have been a descendant of this original Father. Comments in volume XII of The History of Middle-earth associate the Dwarf-cities of the Blue Mountains with two separate clans, the Broadbeams and the Firebeards. Those comments are not absolutely specific about which city belong to which clan, but based on word order, the Dwarves of Belegost and their Lord belonged to the Dwarves known as Broadbeams.