Wikipedia
High-reeve was a title taken by some English magnates during the 10th and 11th centuries, and is particularly associated with the rulers of Bamburgh. It was not however only used by rulers of Bamburgh; many other places used the title, e.g. there was an Ordulf "High-Reeve of Dumnonia".
The first reference to a "high-reeve" was perhaps in the third code of Edmund I of England, where there is an official known as a summus praepositus. Alfred Smyth thought heah-gerefa was influenced by the Scottish word mormaer, the meaning of which, supposedly "Great Steward", is possibly similar.
In the North People's Law, a high-reeve is given a wergild of four thousand thrymsas, the same as a hold and half the wergild of an ealdorman. Ann Williams believes that the High-Reeve was originally an urban official whose job was to deputise for an ealdorman, but unlike other such figures could lead provincial armies.