he pays his debt to the person he serves
In a feudal system, a serf would remain a serf no matter how hard they were to work.
A possible antonym of serf could be "free person" or "freeman," as a serf is a person who is bound to the land and essentially owned by a lord, whereas a free person has autonomy and is not bound to servitude.
Peasant/serf
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The pesants
The serf. He was a slave.
hovels (huts)
the kings,serf
Serfs become fat when they eat pigs because that was all they could afford.
To become free
a vassal or a serf google them