Samantha Clayton

An unnamed woman was the subject of an affair with Oliver Queen, causing him to cheat on Laurel Lance. He ultimately got her pregnant, though she was paid to pretend she'd lost it and move away.

Affair with Oliver Queen
When Laurel proposed apartment hunting with Oliver, the girl was the first of two known women that he cheated on her with, the other being Sara Lance, however he accidentally got the girl pregnant. Oliver became distressed when he learned this and told Moira Queen. Later, Moira brought her over to discuss the matter and made her an offer: 1 million dollars to tell Oliver that she had lost the baby and another 1 million to move to Central City and never speak to him again, to which, after some uncertainty, she agreed. Later on the phone she told Oliver the "bad news", and he was relieved that he wasn't going to be a dad, unaware of the truth.

Trivia

 * In the DC comics universe, Oliver illegitimately has a child, Connor Hawke, with a woman named Sandra. Connor would go on to succeed Oliver as Green Arrow.
 * The role is listed on IMDb as "Sandra", but this is never confirmed onscreen, hence the unnamed nature of the character.