A knight-villein[1] (Cavaleiro-vilão[2] in Portuguese, caballero villano in Spanish) was a free plebeian horsemen who owned land, weapons and a horse, despite not being part of the nobility, being prominent in medieval Portugal, Castile and Leon.
Knights-villein provided military service directly to the king, and in exchange were entitled to the same set of privileges as minor nobles for doing so: among others, they did not pay scutage, and their testimony was considered proof in courts.
[2] The town charter of Penela reads: "all those that dwell here and have two yoke of oxen and ten sheep and two cows and a bed of cloth, he that has more, let him get also a horse".
[2] In medieval Portugal, two-thirds of knights-villein were obligated to partake for a set number of weeks in a fossado (raid) on Muslim territory, being entitled to a share of captured loot, but fined 15 soldos if they did not respond to the call to arms in case of foreign invasion.
[4] They often organized raids on Muslim lands of their own initiative, and settled in or around the frontier towns in southern or eastern Portugal, giving them a military character.