Nebula

Nebula is the secondary antagonist of Guardians of the Galaxy and an anti- hero in Guardians of the Galaxy Vol. 2. 

Personality
Like Gamora, Nebula hates her father for turning her into a weapon. However, she does not seem to want redemption like her sister does and is bent on revenge on Thanos for turning Nebula and Gamora into weapons. She was knownt o be overly jealous, as she hated whenever Thanos expressed Gamora being the evil Titan's favorite daughter.

Physical Appearance
Nebula is a very tall woman, and appears to be taller than Peter Quill. It is assumed Nebula is younger than Gamora based on each other's attitudes, but this has yet to be confirmed. She appears to be in her late twenties, early thirties.

Nebula has dark blue skin that looks purple. Two sides of her face are blue. Her left side, however, has silver metal surrounding her left eye. She also has one arm made of flesh while the other one is made out of machinery.

Early History
"My father would have Gamora and me battle one another in training. Every time, my sister prevailed. My father would replace a piece of me with machinery, claiming he wanted me to be her equal. But she won. Again, and again, and again, never once refraining."

- Nebula to Kraglin Obfonteri Nebula was born on the planet Luphom to unnamed parents. However, Thanos killed her parents in front of her and took Nebula. Since her childhood, Nebula was molded into being a weapon and one of Thanos' personal assassins. When she was young, Nebula at first relied upon Gamora, as she was the only one who could give Nebula what she always wanted: a sister when facing Thanos. However, the two sisters were forced to battle one another in training with Thanos watching with glee. Nebula came to resent Gamora, as she was all the family she had left, but Gamora turned away from her. The grudge would last for many years.

Gamora
Nebula does care for Gamora, in her own strange way, and was the only sibling Nebula hated the least

Corvus Glaive
Corvus is Nebula's adoptive brother. However, Nebula despised him along with her other siblings.

Cull Obsidian
Cull is Nebula's adoptive brother. However, Nebula despised him along with her other siblings.

Ebony Maw
Nebula's adoptive brother. She hates them more than Gamora.

Proxima Midnight
Nebula's adoptive sister. She has a less-than-perfect relationship with her adopted sister.

Peter Quill
Though not getting along, Nebula does find him kind of irritating.

Comics

 * Nebula claims she is the alleged granddaughter of Thanos in the original comics. However, she was changed to being his adopted daughter in the MCU.
 * Nebula's appearance in the movie seems to be based more on her second incarnation from the comics.