Well for one, she is not a Guardian. She was not given the power of the Traveler's light. However, this is what I think she is. Call me dumb, but I think he is a personified version of the Guardians' fates. She pushes you through things. She makes you go to Venus, and she made you go to the Black Garden. At the end, she disappears, never to be seen again. Meaning that the Guardian now has full control over what they do next. Which could also mean that Guardians are puppets, and this Stranger is the puller of the strings. You go through the game questioning nothing. Why are there murderous robots? Why aren't you surprised you came back to life? Why was your Ghost looking for you? Why do I have to go to Venus? Why should I go to the Black Garden? Why am I fighting the Darkness? Who are the Darkness? Is it the Traveler's evil twin? You question nothing. You are given orders, you follow them. You have no control on how things will end. You can do the same strikes or missions 500 times and they will always end the same