The term "Spectre" comes from an abbreviation of the division's official name, Special Tactics and Reconnaissance. The Spectres were assembled during the Krogan Rebellions, and composed of elite asari huntresses and salarian STG operatives, designed to serve as the Council's first line of defense and given broad powers to operate by their own discretion without the hassle of red tape. The first Spectre was the salarian Beelo Gurji, an STG operative who became the subject of much criticism after a crucial mission where he used 30 civilians as bait to lure a target out. The Council deemed that Beelo's whatever-it-takes approach to problem-solving was just what they needed to counter the growing krogan problem, and thus he was appointed in 693 CE.
Spectres are selected from the best military or law enforcement candidates their race has to offer. Given their status, Spectres are living representations of their race's political power, and as such only the most powerful of the Citadel races have had Spectres selected from their ranks. Until the year 2183, Spectres were exclusively turian, asari or salarian, but humanity's growing clout was recognized when Commander Shepard became the first human Spectre.
Spectres have tremendous powers of discretion, able to operate in any manner they feel necessary, and officially above any and all laws with the exception of the Council's dictates. They are held in equal parts awe, respect and fear; cinematic representations of Spectres portray them as super-agents with the fate of the galaxy in their hands, but many critics see their powers as a shortcut to corruption, and deeply distrust any member of the group.
Notable Spectres include:
Nihlus Kryik: The first Spectre introduced in the Mass Effect franchise, Nihlus was a turian operative instructed by the Council to observe Commander Shepard on Eden Prime to judge whether Shepard was a suitable candidate for induction into the ranks of the Spectres. On Eden Prime, however, Nihlus was betrayed and executed by fellow turian Spectre Saren Arterius.
Saren Arterius: One of the youngest soldiers to ever become a Spectre when he was inducted, Saren quickly acquired a reputation for ruthless --- often heartless --- expediency in the service of the Council's goals. In 2183, he betrayed the Council and led the Reaper called Sovereign to the Citadel, ultimately losing his life in a final confrontation with Commander Shepard.
Commander Shepard: Shepard is the protagonist of the Mass Effect franchise, and the first human Spectre.
Tela Vasir: An asari Spectre who secretly also owes allegiance to the Shadow Broker. On the orders of the Broker, Tela has the Dracon Trade Center bombed in a failed attempt to kill Liara T'Soni when she gets too close to uncovering the Broker's identity. She is killed in a fight with Shepard and Liara after her true loyalties come to light.
Jondum Bau: A salarian Spectre who serves as the group's unofficial spokesman during the Reaper War. Bau has spent years trying to capture the master thief Kasumi Goto, but nonetheless admires her skills and greatly respects her as a person.
Ashley Williams/Kaidan Alenko: Whichever one of Shepard's Alliance allies survived the confrontation with Saren on Virmire becomes the second human Spectre in 2186.
Blasto: Blasto is not a real Spectre, but a fictional character in an eponymous film franchise that is hugely popular in the Mass Effect universe. In the films, he is the galaxy's first hanar Spectre, reputed to have "a lover in every port and a gun in every tentacle", known for his catchphrase "Enkindle this!". Later installments of the franchise such as Blasto Goes to War and Blasto Cures the Genophage are ripped from real events, attributing Commander Shepard's heroics to Blasto instead.
Cerulean Star: Also not a real Spectre, but a fictional asari movie star from the Blasto franchise who uses her celebrity to keep her Spectre status under wraps. She teams up with Blasto in the installment Blasto: Eternity is Forever.