Initially, as a familiaris and possibly distant relative of the powerful Kőszegis, he did not involve in the conflicts of civil war which characterized the Hungarian kingdom in the first two decades of the 14th century.

He belonged to Charles's "new aristocracy", who supported the king's efforts to restore royal power after half a century of feudal anarchy.

According to his 19th-century biographer Antal Pór, Alexander Köcski was born into a family of castle warrior origin, which resided in Köcsk, Vas County.

[3] Historian Pál Engel, however, considered that Alexander Köcski individually adopted his seal following his decisive victory over his ardent enemies, the Kőszegis, as a prominent general in Charles' unification war against the oligarchic domains.

[4] Alexander Köcski was first mentioned by contemporary records in 1309,[3] when, near Köcsk, bought portions in Hetyesomlyó, Hetye and Peresztegalja from a local noble family.

[8] During that time, he was considered a familiaris of the Kőszegi family, who de facto ruled significant parts of Transdanubia, including Vas County, independently from the royal power.

Therefore, he did not participate any military campaign during the era of Interregnum, when a civil war between various claimants to the throne—Charles of Anjou, Wenceslaus of Bohemia, and Otto of Bavaria—followed Andrew's death and lasted for seven years from 1301 to 1308.

[9] Andrew Kőszegi, the head of the family responded it with a cruel revenge: he sent his familiaris Solomon the Red with a marauding army to Gerse, where Köcski's brother-in-law Ladislaus Nádasd and his three servants were killed in the local church, which was burnt down too.

[10] When Stefan Uroš II Milutin captured the Hungarian-proxy ruler Vladislav and invaded the Syrmia, Charles I launched a counter-campaign across the river Száva and seized the fortress of Macsó (present-day Mačva, Serbia) in the winter of 1317.

[13] On 3 May 1318, when Köcski was first referred to as castellan, he was granted the lands of Sebes, Takács and Egered in Sopron and Győr counties by Charles I, as a compensation for his earlier heavy losses.

One of his unlawfully acquired castles, Várna (or Óvár, present-day Starhrad, Slovakia) in Trencsén County was returned to its original owners, the Zólyom kinship.

[20] Sometimes after 1321, Charles also donated the castle of Beszterce (today Považský hrad in Slovakia) to Köcski, who was first referred to its castellan in early 1324, few months before his appointment as Judge royal.

[22] Following a few months period of vacancy, Köcski elevated into the position of Judge royal in the week between 26 September and 3 October 1324, replacing Lampert Hermán, who died in office in July 1324.

[24] Köcski and his court resided in Visegrád, after Charles I moved his capital from Temesvár (present-day Timișoara in Romania) to the centre of his kingdom in 1323, when he defeated the last powerful oligarchs.

For instance, he chaired an ad litem court, which made a judgment on a case of ownership of Felvinc (today Unirea, Romania) in favour of the Esztergom Chapter against the Székelys of Kézd Seat.

A certain Michael acted as Köcski's pristaldus (royal commissioner or "bailiff") in 1326, while Nicholas Gősfi served as a collector of the judicial fines in 1325.

Over his newly acquired land, Köcski and his descendants were granted full jurisdiction, including ius gladii ("right of the sword") within the boundaries of his estates.

[29] Continuing the method of his predecessors in the early 14th century, the usage of material evidences during the litigation processes became widespread under Köcski's term, pushing back those traditional practices of justice, like trials by ordeal and combat.

During the military campaign, Köcski seized Sárvár, Németújvár (present-day Güssing, Austria) and two other forts in Kőszeg from the rebellious John Kőszegi.

Charles provided him broad power in the redistribution of lands to the loyal local nobility and he had the mandatory of royal grace to the Kőszegis' former familiares.

He compiled his last will and testament on his deathbed in the presence of Archbishop Ladislaus Jánki, Master of the treasury Demetrius Nekcsei and Ban Mikcs Ákos.