Short answers, pulled from the story.
Triptolemus was a young boy from the palace of Eleusis who became a hero and priest of Demeter. He received a chariot drawn by winged dragons and seeds of wheat and barley to teach agriculture across the earth.
Metanira stopped the process while Demeter intended to make his son Demophon immortal through the same fire ritual. Instead, Demeter chose Triptolemus for her special gift because she found him weak and dying before restoring his strength with breast milk.
King Lyncus planned to kill Triptolemus out of envy but Demeter intervened to save her student. She transformed the jealous king into a lynx as punishment for his attempt to claim all praise for the new agriculture.
Triptolemus flew toward Scythia to teach King Lyncus how to grow food and later traveled to Patrae near the river Peirus. He also taught the Pelasgian people known as Arcadians and founded settlements like Aroe and Antheia in memory of those who died.
Socrates names Triptolemus as one of the judges who rule over the afterlife alongside Minos Rhadamanthus and Aeacus sons of Zeus. Each judge holds specific territory within the underworld realm where Triptolemus holds authority over the dead initiated into the mysteries.