- “I'm a magical princess from another dimension!”
- ―Star introducing herself to Marco
Star Butterfly is an intergalactic princess from the Kingdom of Mewni, who has been sent to Earth by her parents to live a normal life, after many years of fighting evil in space. While on Earth, she lives with the Diaz family, and takes Marco Diaz on adventures in other dimensions, and in battles with monsters.
Star is extremely energetic and friendly. She loves having fun, and she usually has an optimistic outlook on life. She loves to help others and whenever she sees that someone is upset, she does her best to cheer them up. She is a bit reckless, as she enjoys fighting monsters and doing wild things. Strangers, in her eyes, are just friends she has not met yet, and she feels bad if she hurts someone's feelings, whether intentionally or not. However, Star can be egocentric, wanting attention and getting frustrated with things that bother her. Thus, she gets jealous very easily. Star has a happy-go-lucky attitude and always puts a smile on everyone's faces. She also works very hard towards her goals, so much that she will sometimes go sleep-deprived.
- In earlier conceptual versions of the series, Star was originally a grade schooler who did not have magic powers, but believed she did. After some suggestions on making Star older and have real magic powers, Daron changed her into a princess from a different dimension.
- Star Butterfly's character was influenced by many female characters Daron Nefcy admired in Japanese TV shows. Such as the heroines of Sailor Moon, Magic Knight Rayearth and Revolutionary Girl Utena.
- Daron Nefcy originally wanted Star to be a fourth grader but executives wanted the character to be a little bit older.
- In the episode "Cheer Up Star", she is revealed to have coulrophobia (a fear of clowns).
- Star is the first Disney Heroine to have coulrophobia, with the second being Riley Andersen.
- In the episode "Diaz Family Vacation", it is revealed that she inherits her passion to fight monsters from her father, who secretly fights monsters himself.
- The heart marks on her cheeks can change into other things to reflect her emotions.
- Cracked Hearts - When she is crushed or irritated.
- Light Bulbs - When she suddenly comes up with an idea.
- Hourglasses - When she is bored.
- Skulls - When she is angry.
- In the episode "Royal Pain", Star implies that she and other people from Mewni are not humans when she tells her father "Humans put things in there and flush them down." when he inquired about the toilet. This could also explain in "Mewberty" when she went through her metamorphosis and why she has butterfly wings now.
- She later states in the episode "Mewnipendance Day" that she is a "Mewman", humans who live on Mewni.
- She dressed up as Ludo for Halloween in "Hungry Larry".