Final Fantasy VII
Do The Jobs You Hate
The Turks are effectively ShinRa's Black Ops department, as they are in charge of doing the majority of dirty underhand work. Officially, they are the Investigation Sector of the General Affairs Department.
In Final Fantasy VII, The Turks are lead by Tseng, with the assistance of Reno, Rude and their new recruit, Elena. While they aren't integral to the story, they help to drive it along by performing some horrible deeds that have been ordered by their superiors. The first of these deeds is the combined capture of Aeris Gainsborough and the destruction of Sector 7.
Losing Their LeaderThe Turks' next job is to investigate the Temple of the Ancients, but it ends badly and Tseng is badly wounded. This leaves just Reno, Rude and Elena as the only known Turks in Final Fantasy VII.
Following the demise of ShinRa, Reno decides that they no longer care about the activities of Cloud and his group. They decide to follow their own orders and become their own bosses.
Final Fantasy VII: Advent Children
Back To Business
All four of the Turks that appeared in Final Fantasy VII also appear in Advent Children. However, due to ShinRa no longer existing, they technically aren't Turks anymore. Even so, they do still work for Rufus ShinRa and act as his bodyguards.
Their initial involvement sees Tseng, Elena and Reno extracting Jenova's remains from the Northern Crater. This doesn't end well though, with Tseng and Elena being kidnapped by Sephiroth's Remnants. Fortunately, they are rescued by Vincent and come to Rufus' aid when they are needed.
A Change In RoleDue to Rufus' new outlook on life, he uses the Turks to perform good. Although their primary role is to protect him, the Turks also fight against the Silver Haired Men and even manage to defeat both Loz and Yazoo, even though they are heavily out matched.
This was their last appearance in a Final Fantasy VII title though, as they did not feature in Final Fantasy VII: Dirge of Cerberus.
Before Crisis: Final Fantasy VII
Premiere Recruiting Agency
One of the Turks' roles is to recruit new candiates for SOLDIER; often by use of force or extreme "persuasion". The amount of Turks present in Before Crisis greatly exceeds that seen in the other games as ten playable characters were also included.
Before Crisis also sees multiple changes in leadership for the Turks, as Verdot, Heidegger and Tseng all take charge at various points. Verdot's reign is quite crucial to the story in the game as they fight against AVALANCHE, an eco-terrorist group.
Crisis Core: Final Fantasy VII
Working Side By Side With SOLDIER
The Turks are employed in Crisis Core as more equal to SOLDIER, as they are often sent along to assist with their activities. This doesn't always work out well though, as some Turks are killed during an investigation into the activities of Genesis.
Despite orders to capture Zack towards the end of the game, both Cissnei and Tseng show that they don't blindly follow orders as they allow Zack to slip through their fingers. Towards the end, Tseng even orders the Turks to bring him in safely before the ShinRa army finds him, but unfortunately they are too late.