I’ve just finished a PhD on the depiction of Norse speakers (Vikings) operating in Ireland in Middle Irish (Gaelic language) dynastic propaganda texts. Because this was opportunistic slavery rather than specifically racist slavery, there is a chance that an individual could “own” a slave who later gained their freedom and enough wealth and power to “own” their former owner, but it would require a drastic change of fortune on both their parts.

The most famous of the texts I study, Cogadh Gáedhel re Gallaibh (War of the Gael against the Foreigner), paints the Norse takeover of Munster (southwest Ireland) as complete, where virtually all Gaels are enslaved or in crushing debt to the Norse. Then when the hero of the text, the historical Brian Bóroimhe (Boru), rallies the Gaels of Munster to rise against the Norse, the success is so complete that now all the Norse are in bondage to Gaels - there’s a line about no quern (grain-grinding stone) without a foreign woman working it.

Now, that said, this text was written for a descendant of Brian and plays very loose and fast with history (hence ‘dynastic propaganda’). The actual situation on the ground was probably not as dramatic as depicted, but it’s certainly possible that a slave owner and slave could switch roles over a long lifetime of changing political fortunes.

Seán Duffy’s Brian Boru and the Battle of Clontarf is the best general reading book out there on this phenomenon, but I’d be happy to recommend more specific scholarly articles on Norse and Irish relations if desired.