Stranger (Korean: 비밀의 숲), also titled The Forest of Secrets, is a South Korean crime thriller television series created by Choi Jin-hee created and written by Lee Soo-yeon. Consisting of two seasons of sixteen episodes each that first aired on 2017 and 2020 respectively on tvN, it was written solely by Lee Soo-yeon, with Ahn Gil-ho and Yoo Je-won acting as directors for season 1, and Park Hyun-suk for season 2.

Both seasons feature Cho Seung-woo and Bae Doona as a prosecutor and a policewoman whose dedication and relentless pursuit of the truth lead to form an unlikely alliance dedicated to exposing criminals, including the corrupt officials within their own respective organizations. It co-stars Lee Joon-hyuk, Yoo Jae-myung, Shin Hye-sun, Yoon Se-ah, Jeon Hye-jin and Choi Moo-sung among a large cast of characters mostly belonging to the Ministry of Justice or South Korean police.

The series was a hit with both domestic and international viewers, and received favorable reviews for its tight plot, gripping sequences and strong performances. It was featured on New York Times list of Best TV Shows of 2017, and won several awards including the Grand Prize for television at the Baeksang Arts Awards. A spinoff series focused on Lee Joon-hyuk's character, titled Dongjae, the Good or the Bastard, premiered in 2024.