Mardil (Q. ‘Friend of the House’), the eldest son of Steward Vorondil (the Hunter), was the first Ruling Steward of Gondor (TA 2050-80). He had been the Steward of King Eärnil II and King Eärnur, and had dissuaded the latter from accepting the Lord of the Nazgûl’s challenge. But in 2050, King Eärnur could not be restrained, and when he rode to Minas Morgul and never returned, Mardil took up rule of the South-kingdom (with the approval of all) to prevent civil war among the royal family.
Mardil was a wise ruler who helped ease the South-kingdom through the transitional period that followed after the disappearance of Eärnur. At the same time, he brought great honour and renown to his own House, and it was he who introduced the Stewards’ Reckoning, a series of minor changes to the King’s Reckoning calendar system. (This calendar was eventually adopted by most of the Westron-speaking folk of Middle-earth.)
Because of his faithfulness, he was called Mardil Voronwë, the Steadfast. For almost a thousand years after his reign, the Ruling Stewardship passed to Mardil’s heirs, but in all that time, no Steward ever called himself King.