His weapon of choice for contracts is magic, stating that "there is a spell for every circumstance." He is the self-described "cranky old uncle who nobody talks to" of the Dark Brotherhood family at the Falkreath Sanctuary.
When asked about himself, he says he was a "child prodigy." Casting simple spells by one, completing complex incantations by three, resurrecting corpses by seven, and accidentally burnt down his family home by the age of thirteen due to some lightning that got "out of control" but he says nobody should worry, because he mastered all magic just after that happened.
He then went on to teach at the College of Winterhold for two years, but left due to none of the mages there "truly appreciating the Destruction school." This led him to join the Dark Brotherhood. When asked for help about a contract from Nazir, he says that methods used today are overrated and follows up with, "Just do what I do. Walk up to them, introduce yourself, melt all their skin off, and run like the wind. Works every time." He is also the first member to welcome Cicero into the sanctuary.
If asked for advice during Bound Until Death, he will reveal that he was married at one point, but murdered his wife during their honeymoon over the temperature of his bath water.
At first Festus is rude and arrogant towards the Dragonborn, but upon following his instructions in the Recipe for Disaster quest, he says, "I believe I was wrong about you" and he gives them the Nightweaver's Band.
When the Dragonborn returns to the Sanctuary during the Penitus Oculatus attack, Festus is the first of the Dark Brotherhood that is found, his face hidden by the twenty arrows pinning him to a tree.
- Festus may be a reference to two characters who share his name from the Fallout series, which Bethesda have contributed to.
- "Festus" is Latin for "joyous" or "happy."
- After being found dead at the Sanctuary, his shrouded outfit cannot be taken from his body.
- After speaking to the other guild members about his recent contracts, Festus will often make a comment about how they are a "young pup" and that he is more experienced because of his age. He will make these comments even to Babette, who is actually the only member of the Dark Brotherhood older than Festus, being over 300 years old.
- Festus is voiced by Jim Cummings, the voice actor for Minsc in the Baldur's Gate series.
- At first glance, Festus will be kind to the player when they are revealed as Listener, but later it is revealed that he is jealous to their relationship to the Night Mother, having wanted to be named Listener himself.