Thanks to VTer quartinb (Vitor) for clearing this up.
He writes: "it belongs to NUNO ALVARES PEREIRA, the "commander" of portuguese troops and the
man responsible, strategic wise, for the great victory in ALJUBARROTA
BATTLE, the real turning point against the Spanish occupation towards PORTUGAL.
D:JOAO I , Mestre de Avis ,was the king of Portugal and he decided to build the
monastery because of that great victory against Spain outnumbered and much
more armed than the Portuguese army"

