Dream Messengers are a form of highly advanced and invasive magic used to send deliberately fabricated, vivid dreams or visions directly into another person's mind. The recipient experiences these visions as if they were real events, making this a powerful tool for psychological manipulation. This phenomenon is not a common form of magical communication but rather a specific, weaponized application of Legilimency, the art of navigating another's mind. It relies on a strong pre-existing mental connection between the sender and the recipient. In the case of Lord Voldemort and Harry Potter, this connection was created and sustained by the fragment of Voldemort's soul residing in Harry, which turned him into an unintentional Horcrux. This link allowed Voldemort to exploit Harry's mind, particularly when Harry's emotions were running high and his mental defenses were low.
The primary function of a dream messenger is to implant a false narrative into a target's subconscious. The sender constructs a detailed scenario and projects it into the sleeping target's mind. The goal is to provoke an emotional response and compel the target to act on the false information upon waking. Lord Voldemort weaponized this connection during the Second Wizarding War. Initially, the connection was uncontrolled, allowing Harry Potter unwanted insight into Voldemort's thoughts and actions, such as the attack on Arthur Weasley. However, Voldemort soon realized he could control the flow of information. He began planting visions to manipulate Harry, understanding that Harry's loyalty and impulse to save others were his greatest weaknesses. The primary defense against such mental intrusion is Occlumency, the magical art of closing one's mind. Albus Dumbledore instructed Severus Snape to teach Occlumency to Harry specifically to counter this threat. Harry's difficulty in mastering the discipline, fueled by his animosity towards Snape, left him vulnerable to Voldemort's ultimate trap.
The use of dream messengers is a central plot point in Harry Potter and the Order of the Phoenix. Throughout the school year, Harry Potter experiences increasingly vivid visions from Lord Voldemort's perspective.
This event directly instigated the Battle of the Department of Mysteries, which had several crucial consequences, including the death of Sirius Black and the public confirmation of Lord Voldemort's return. Following the battle, after Harry's mind briefly merged with Voldemort's, the Dark Lord became aware of the dangers of their two-way connection and subsequently sealed his mind from Harry.
Dream messengers serve as a critical plot device that drives the climax of the fifth book. They are the ultimate expression of the unique, dangerous connection between Harry Potter and Lord Voldemort.