Tegan first appears in the Fourth Doctor's last serial, "Logopolis".

Entity and relation annotations:
id: 0
type: entity
value: text: Tegan
labels: <Person>
id: 1
type: entity
value: text: "Logopolis"
labels: <Work_of_art>
type: relation
to_id: 1
labels: Person:is_character_in:Work_of_art
from_id: 0