Triptolemus

Triptolemus is the god of farming; he aided Demeter when she was searching for her daughter, Persephone, who was kidnapped by Hades. He appears in The House of Hades.

The House of Hades
When Hazel Levesque, Frank Zhang, and Nico di Angelo were attacked by katoblepones, Triptolemus protected them from harm on his home. When Nico told him that he was a son of Hades, Trip became angry and turned him into a corn plant. Trip is a friend of Demeter, so Nico being a son of Hades was insulting, as Hades had abducted Persephone, Trip's sister. Frank tried to convince Trip to heal Hazel and turn Nico back to normal, but Trip refused, even though they had brought him back his book. Trip declared that he would only help them if Frank found him another serpent to power his flying machine.