Clan Mroranon has always been the largest and strongest of the ruling clans. The mythical Mroranon is said to have been the son of the last king of the Realm Below, and to have rallied the exiles to establish the Mror Holds. Talespinners say that it was Kol Korran’s bargain with Mroranon that ensured prosperity for the dwarves, and Krona Peak is home to both the Iron Council and Kol Korran’s Throne, the largest temple dedicated to the Sovereign in Khorvaire.
While Mroranonhold has a wide variety of mines, it’s best known for iron and mithral. It has established strong ties with House Cannith, though all of the Five Nations import Mroranon steel. It has the strongest general industrial base of the holds, and Krona Peak is the largest single city in the region. Mroranon dwarves are proud of their skills as warriors and negotiators, even if they acknowledge Doldarun and Kolkarun to be the best in those fields. What sets the Mroranon apart is leadership. Mroranon sees the future and inspires others to follow. Mroranon unites, and makes wise decisions for the good of all. This ties to the mythic story of Mroranon as the leader— Doldarun is a mighty champion, but Mroranon has the vision. Mroranon are strong supporters of the Sovereign Host and believe that the dwarves are blessed; many of the most devout Mror priests and powerful adepts hail from Mroranonhold. With the largest and most industrialized territory, Mroranon has the deepest investment in the Realm Below. It has multiple colony outposts, including one tied to a demiplane mine and another holding an ancient fortress, and is holding a firm line while building power for another surge. Mroranon and its vassal clans have recovered many legendary relics and artifacts from the depths. While they don’t oppose symbionts as strongly as Doldarun, they refuse to make use of dularash items and assert that any contact with the daelkyr or their creations is dangerous
Acolyte, noble, and soldier are common backgrounds for Mroranon dwarves. While paladins are more likely to be found in Doldarun, clerics (especially Knowledge, Trickery, or Life), fighters, and bards are all sound choices for Mroranon. With its big cities, it’s also a reasonable option for criminals and rogues.
Source: Exploring Eberron
Mroranon is one of the most powerful clans in the holds, and it lends its founder’s name to the nation as a whole. Its mines produce the best iron ore in Khorvaire, allowing Mroranon to build strong diplomatic and mercantile ties with Breland. Mroranon seeks the destruction of the Jhorash'tar orcs, who hide in the Ironroot Mountains. The clan has feuds with Clan Kolkarun, which uses its mineral wealth to undercut Mroranon’s iron trade; with Clan Soranath, whose founder quarreled with Mror in times of legend; and with Clan Toldorath and Clan Tordannon, who seek to grant the Jhorash’tar the full political power of a Mrorian clan.
Source: Player's Guide to Eberron
During the Last War, Mroranon was closest with Breland and Karrnath.
Source: The Forge of War