Harbinger

"Human, you've changed nothing. Your species has the attention of those infinitely your greater. That which you know as Reapers are your salvation through destruction."

Harbinger is a Reaper, who resides in dark space with the rest of the Reaper fleet.

During the events of Mass Effect 2 Harbinger is the mastermind behind the Collectors, appearing to permanently possess the Collector General, having them abduct the entire population of human colonies in order to use their genetic material to create a Human-Reaper. While controlling the Collector General, Harbinger is capable of possessing any individual Collector, often doing so when the Collectors are engaged in combat with Commander Shepard. While controlling a Collector, Harbinger is able to speak through them, usually to command other Collector troops, or threaten its opponents.

After Commander Shepard's team assaults the Collector base and destroys the still incomplete Human-Reaper, Shepard can either destroy the base completely, or purge the base of all life. Both options will result in Harbinger relinquishing control of the Collector General and vows that the Reapers will "find another way." Either way, the Collector General is destroyed in the blast.

After the destruction of the Human-Reaper, Harbinger and the rest of the Reaper fleet are seen in dark space; all of which reactivate and head toward the Milky Way.

Trivia

 * If Garrus is in the squad while Harbinger is controlling a Collector it will state "Turian, you are considered too... primitive."
 * If Grunt is in the squad while Harbinger is controlling a Collector it will comment on the krogan species as "...wasted potential".
 * If Samara is in the squad while Harbinger is controlling a Collector it will comment on the asari species as "weak" because they rely on other species to reproduce.
 * If Mordin is in the squad while Harbinger is controlling a Collector it will state "Salarian, life span too short, genetic code too fragile."
 * While in possession of a Collector, Harbinger shows a personal interest in Shepard by sometimes saying, "Preserve Shepard's body if possible," "you will feel pain, Shepard," "I know you feel this, Shepard," "focus on Shepard," "neutralize Commander Shepard," "if I must tear you apart, Shepard, I will." This shows that both the Reapers and/or Harbinger are aware of Shepard's actions against Sovereign and the geth, and have an interest in retrieving the Commander's body for unknown reasons, possibly for Shepard's genetic material, as Shepard is of the species that destroyed the Reaper vanguard Sovereign. This makes Shepard, and humanity as a whole, very appealing to the Reapers.