What saint's feast day is on August 21?

The following saints are memorialized on August 21:

Abraham of Smolensk

Anastasius Cornicularius

Aria

Avitus I of Clermont

Bassa and Companions

Bernard Tolomeo

Bruno Zembol

Cameron

Cyriaca

Gilbert

Hardulph

Joseph Nien Vien

Ladislaus Findysz

Leontius the Elder

Luxorius

Maximilian of Antioch

Our Lady of Knock

Our Lady of Prompt Succor

Paternus

Pius X, Pope

Quadratus

Sidonius Apollinaris

Victoire Rasoamanarivo