Arin Sur is the sister of the Green Lantern Abin Sur, and the wife of Sinestro.
Arin Sur was the sister of Abin Sur, a legendary member of the Green Lantern Corps. Eventually, she fell in love with and became betrothed to her brother's best friend, Thaal Sinestro. They had a child together, who they were forced to give up for adoption, named Soranik Natu. Eventually, her husband was accused of being a tyrant on his native Korugar, and by tragic circumstances Arin somehow died. Her death largely inspired him to sever emotional ties with the world, and stop acknowledging any emotion for anything. She was the only woman he ever loved, and his feelings for her are one of his greatest kept secrets.
Arin Sur is featured in the flashbacks that showcase Sinestro's rise and fall, along with their child, Soranik. Arin would hide Soranik somewhere on the world, far from her father's reach and influence. Some time later, Sinestro would discover her body in their room sometime after they occupied the home of the former government.
Though Sinestro claims she was killed by dissenters from the council of leaders he exiled, the flashback implies she killed herself, unable to deal with the monster her husband was becoming. The grief Sinestro felt from the loss of his wife and child caused him to become even more tyrannical, ultimately culminating in his removal from the Green Lantern Corps.