Appointed by the ruler, the count of Székelys (székelyispán or comes Siculorum) was the principal (or leader) of the self-governing Transylvanian Székelys. The study seeks to reveal the extent to which the era of Sigismund of Luxembourg (1387-1437) represented a separate stage in the history of the office of count of Székelys. The first part of the essay discusses the appointment of the various holders of the post, the duration of their office, and the political circumstances that influenced their work. During the initial period of Sigismund's reign, the baronial league led by János Kanizsai exerted considerable influence upon the king. Accordingly, most holders of the office of count of Székelys were appointed from among this group. Once the king had strengthened his position, however, even an uprising by the league was unable to stop him. Indeed, from 1404, the king managed to consolidate his system of government, with the assistance of the Cillei-Garai group of barons. During this period, appointments to the post reflected the wishes of the king and the group of cooperative barons forming the mainstay of regal power. The fact that two officeholders - Mihály Nádasdi (1405-1422) and Mihály Kusalyi Jakcs (1426-1438) - dominated the 33-year period between 1404 and 1437 is indicative of the degree of stability. Sigismund attempted to counterbalance the powerful Transylvanian voivodas by extending the territorial jurisdiction of the count of Székelys. The death of the emperor-king was quickly followed by the collapse of the power structures. Still, as far as the office of count of Székelys was concerned, the early part of 1441 was the real dividing line, when János Hunyadi and Miklós Újlaki unified for the first time the authority of count and voivoda - although it was still only a temporary development at this point. The second part of the study examines the consolidation of the holding of the office by several nobles, the manner in which the fortresses constituted the count's honor, changing military roles by way of reaction to the Turkish threat, problems arising from the development of Székely country boroughs, increasing social tensions among the Székely population, and the alliance in 1437 of the three Transylvanian nations, signifying the root of the peculiar Transylvanian system of order - whose conception was assisted by the counts of Székelys. The period between 1387 and 1441 was a distinctive period in the history of the office of count of Székelys. It may also be called the last 'classical' era, because the next period, the Hunyadi era, saw the final merger with the post of voivoda and the abandonment of the separate office of count of Székelys in 1467.