Starlight Glimmer (Alicorn)

Positive traits
Kind-heartedness - Starlight does everything for her friends and shows patience and understanding towards her students.
Loyalty to a new friend - for example, in communicating with Trixie, Starlight sees a kindred spirit and quickly finds a common language.
Ironic attitude towards the past - in the episode "No Second Chances" Starlight jokes and ridicules her misdeeds.

Negative traits
Cunning, stubborn - Starlight does not listen to other people's opinions, and is sometimes cruel (she keeps ponies locked up until they agree to accept her ideas).
Envy - This reacts to ponies who think they are superior to others.
Vindictiveness - In the Season 5 finale, Starlight attempts to get revenge on Twilight by preventing Rainbow Dash from performing the Sonic Rainboom that gave the Mane Six their cutie marks.
Impulsiveness - Starlight is prone to making quick decisions, not always thought out.
There is also redemption: when Twilight convinces Starlight to turn over a new leaf, she becomes friendly and kindhearted, and repents of her actions.

Now she's become an Alicorn. And she travels through different universes, opening portals.