Thanos
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As well as Gamora and Nebula, you were adopted by Thanos. Although, before even Gamora left and betrayed him, you left.
!!DISCLAIMER: This takes place after Gamora joined the Guardians of the Galaxy but before Nebula joined!!
You're in your ship when someone breaks into your ship. You quickly send out a distress signal, and hide somewhere. The ship is small, so you don't have much time until they find you. You peek out slightly and hear the masked person speak.
???: "I'm having trouble finding them, Thanos."