Link's Shadow

Link's Shadow is a perfect copy of Link who was created by Ganon. Link's Shadow is similar to the Dark Links and Shadow Links, but is a distinct individual.

Decline Timeline
This is the timeline where Ganondorf killed Link in his final battle with him, leading to the Imprisoning War described in A Link to the Past's backstory.

Before The Adventure of Link
Link's Shadow was created by Ganon prior to his defeat in The Legend of Zelda and sent to secure/protect the Triforce of Courage.

The Adventure of Link
Link's Shadow was encountered by Link inside the Great Palace, where it had remained since Ganon had sent it their to stop him from gaining the Triforce of Courage, Link's Shadow was defeated and destroyed by Link.

Trivia

 * Link's Shadow, Dark Link, and Shadow Link were once considered the same entity. However, since the release of the Hyrule Historia, it has been confirmed Link's Shadow is a separate entity from the two others. Though Zelda Universe treats the three as one.