A hacker who spent her life looking for the people who left her, found them, and did not like the answer.
Daisy Johnson was born in China to Calvin Johnson and his Inhuman wife Jiaying, and was taken by S.H.I.E.L.D. agents as an infant and raised as an orphan by nuns. Under the name Skye she became a hacktivist who worked against organisations like S.H.I.E.L.D., which is how Coulson finds her and recruits her, and has Ward and then May train her into a field agent.
She is the reason to watch Agents of S.H.I.E.L.D. at all. Seven seasons is long enough to actually change somebody, and Chloe Bennet’s arc from a girl living in a van to Quake is the longest continuous character journey in this catalogue, film or television.
Minor spoiler
The search for her parents ends with the Inhumans, with Terrigenesis, and with a mother who would rather have a weapon than a daughter. Her powers cost her the family she spent her life looking for.