Ealdormen were appointees of the king and were originally mostly from the ancient and powerful families, but later were often chosen from among the king's comites (plural of comes, lit. "companion") and many, especially in the early Danish period, were new to high office. When smaller kingdoms such as Sussex and Essex were absorbed within a larger one, e.g. Wessex, the former ruling family seems to have been suffered a diminution of their title from "King" or "Sub-King" to Eorldorman. Presumably this office would have initially been hereditary among the former royal family but in later Anglo-Saxon times the office was clearly not hereditary or where it was this was exceptional. There are several examples of tenth-century ealdormen whose sons became ealdormen (if not always of the same district), such as Æthelstan Half-King and Æthelweard the Chronicler.
Towards the end of the tenth century, the term ealdorman gradually disappeared as it gave way to eorl, probably under the influence of the Danish term jarl, which evolved into modern English earl. The analogous term is sometimes count, from the French comte, derived from the Latin comes. The ealdormen can be thought of as the early English earls, for their ealdormanries (singular ealdormanry, same meaning as earldom) eventually became the great earldoms of Anglo-Danish and Anglo-Norman England.
An ealdormancy was an Anglo-Saxon governing body over several shires, made up of more than one ealdorman.
Although earls may be regarded as the successors of ealdormen, the word ealdorman itself did not disappear and survives in modern times as alderman. This term, however, developed distinctly different meaning which have little to do with ealdormen, who ruled shires or larger areas, and aldermen are members of a municipal assembly or council.