Felix was once a slave owned by Caecilius. He appears in Stages 6 and 7 of Book 1.

In Stage 6, Felix punches a guy so good he dies. Caecilius lets him leave after that.

In fabula mirabilis, Stage 7 of Book 1, he (drunkenly) tells a story about his friend seeing a centurion turning into a werewolf in the woods.

Grumio may be the dankest character, but Felix is the most badass.