Although in drama and masterpiece theatre and in literary fiction your main character needs to have both a moral and a psychological ‘need’, that rule doesn’t hold for travelling angel types. Mary Poppins does not have a moral need. (She does not treat other people badly.)
Traveling angel characters are found mainly in Westerns, detective stories and comedies. They are also found in children’s stories.
The travelling angel often enters the storyworld when the storyworld is in trouble. (But not always.) They fix the problems, then move on.
The travelling angel comedy is a comedy of structure and contrast. Other comedic forms rely on comedy of dialogue. Because the comedy is in the story’s structure, critics tend to say a comedy of the traveling angel type has ‘heart’. Audiences love stories with heart and so traveling angel films rarely fail at the box office.
It’s also known as the ‘walking the Earth’ trope.
EXAMPLES OF THE TRAVELLING ANGEL TROPE
- Crocodile Dundee (Australian film) — comedy, adventure
- True Grit — anti-Western, adventure
- Amélie (film) — French comedy romance — traveling angel comedies are popular in France for some reason
- Chocolat (book and film) — drama, romance
- Good Morning, Vietnam (film) — biography, comedy, drama
- Mary Poppins (family musical based on a series of books by P.L. Travers) — children’s book — comedy, fantasy, Nanny Story
- The Music Man (film, musical) — comedy, romance
- Shane (classic Western) — about the only non-ironic Western movie made since the world wars — includes drama and romance
- Anne Of Green Gables — though Anne doesn’t leave Avonlea for good, she is back and forth, and tends to win crotchety people over so long as they are basically good in the first place.
- Santa — the ultimate travelling angel!
Related: Angelic Tropes at TV Tropes