In art, the four evangelists are often depicted by specific symbols. (These may be seen in vault of the baldachin over the high altar at St. Anthony Church.) The symbols come from the Book of Ezechiel who had a vision of God in the midst of four creatures. The Church Fathers saw this as a foreshadowing of the four Gospels.
The creatures reappear in the Book of Revelation.
Matthew’s symbol is a man because he begins his Gospel with the human genealogy of Our Lord.
Mark’s symbol is a lion because his Gospel begins with the John the Baptist in the wilderness.
The ox, an animal of sacrifice, is the symbol Luke’s Gospel since the Gospel begins in the Temple, the place of sacrifice.
The eagle is associated with John since his writing “soars above” as he emphasizes Christ’s divine nature.