|“||The River Lethe in the Underworld, it dissolves your memories, wipes your mind clean permanently. That's the branch of a poplar tree from the Underworld of my father, Hypnos. Lethe is not a place you want to go swimming.||”|
Annabeth Chase takes Jason Grace to Clovis to see if his memory can be restored. When they enter the cabin, Clovis warns Jason not to touch the water dripping from a poplar branch, as it is water from the River Lethe. One touch would cause him even more memory loss, wiping his mind completely clean.
When Annabeth explains Jason's memory loss, Clovis agrees to help. He makes Jason fall into a deep sleep to try and recover his memory. Clovis tells them that his memories may have sunk under the surface of his brain and that with a good sleep he could retrieve them. Once Jason wakes up, Clovis tells him that his memory wasn't suppressed, but a god or goddess has stolen his memories.
Clovis was present at the Camp's campfire, though he was sleeping most of the time.
While Nico is dreaming his dreams, he is interfered by Clovis and the Hypnos Cabin because they dream so powerfully. Nico tells Clovis to inform Thalia Grace that one of Gaea's giants are after him and that he is bringing the Athena Parthenos over. Clovis shows Nico the war meeting that the cabin counselors had.
Clovis is sleepy all the time, or he is asleep. However, he is very knowledgeable about the gods, knowing that their forms are liquid, much like dreams, and having great insight to the gods themselves.
Jason describes him as looking like a baby cow. He has blond hair and a wedge-shaped head and a gentle, bovine face. He has thick features and a thick neck. His body is stocky but with spindly little arms, like he hasn't lifted up anything but a pillow. His breath smells like warm milk. He seems to be falling asleep everywhere and it takes an effort to keep him awake. Drew also describes him as "pretty repulsive."
- Hypnokinesis: As a son of Hypnos, he can control sleep and dreams.
- He has the ability to astral project in his dreams and in a different form like the gods.
- He can see people's memories, even though it failed with Jason, since his memory was taken by a god.
- He and his cabin lull people to sleep.
- Each of his siblings, including him, radiates individually a power that causes people to fall asleep, as when he yawned and Jason and Annabeth yawned after him.
- He can do nearly anything involving sleep as his father is the god of sleep.
- He can see the gods in his dreams, who always shift forms.
- He has an extremely heavy sleep at times, to the point of once not even flinching when Jason strikes a lightning bolt next to him.
- His nostrils are capable of holding twenty colored pencils.
- Clovis is the first demigod in either series that clarifies the difference between the Greek and Roman aspects of the Olympians.
- He has met Michael Jackson in his dreams.