Stefan Delaney is a new recurring character introduced in the sixth season of Stefan's Diaries. Even though he is the son of the doppelganger, he doesn't have supernatural powers or abilities.
Stefan was born to a doppelganger mother and a human father. He grew up in Mystic Falls, and lives in the old Salvatore boarding house, now the Delaney Residence. He has no knowledge of the supernatural.
Without his or his father's knowledge, he is actually named after his mother's greatest love, Stefan Salvatore.
Stefan was first seen in the series premiere Extinct, when his namesake was newly freed from the safe he was locked in and wanted to get back to his home. When he couldn't due to not having been invited in, he looked through the window and saw a kid not older than 10. It was only revealed that he was Katherine's son and his name was Stefan later in the season.
Stefan later became a recurring character in season 6, when he was kidnapped by Ewa, a powerful and vengeful witch. At where he was kept, he met Hayden Mikaelson, Klaus' daughter and an ultimate hybrid, who was also kidnapped. Lacking someone they can count on, they found strength within each other and became close friends.