Eric Sacks was born on an American military base in Okinawa, Japan. His father went to fight in the Vietnam War and was killed, and Sacks grew up as an outsider. He was taken in by Oroku Saki, a sensei who instilled Sacks with a love of Japanese culture and honor. He was particularly enthralled by a story in which an evil warlord who had poisoned the town's water supply was defeated due to a powerful alchemist.
In 1999, Sacks moved to New York City at some point, becoming a wealthy businessman and scientist thanks for founding his successful giant corporation "Sacks Industries". There, he worked alongside a scientist by the name of Dr. O'Neil in creating a "Mutagen", which he had intended to use as an antidote to a plague he and Saki, the Shredder, would unleash on New York. Sacks wished to use the antidote to pretend to be a hero. The mutagen was tested on a rat and four Turtles, but when Dr. O'Neil uncovered Sacks' true plan, he torched the lab to destroy the research. Dr. O'Neil's daughter, April, rescued the test subjects, but the good doctor was killed by Sacks.
Trying to recreate the Mutagen
For fifteen years, Sacks attempted to recreate the Mutagen, but it proved difficult without the project's notes and one of its chief scientists.
In the meantime, Sacks and Shredder had started the Foot Clan, a paramilitary organization, to steal components for the Mutagen and generally spread fear throughout New York City. April, now a lifestyle reporter for Channel 6, attempting to break through to a higher position, begins chasing leads on the Foot. She ends up encountering now anthropomorphic Turtles. Remembering Sacks as her father's kindly boss and seeing his open philanthropy and will to extinguish the Foot Clan, she opens up to him about the Turtles, alerting him of their survival. He begins to formulate a plan with Shredder to capture the Turtles and extract the Mutagen from their blood.
The Turtles take April to meet their father, the former lab rat Splinter, and the Foot Clan track down the Turtles into their Sewer lair. Shredder and the Foot attack them, and bring back three of the Turtles for extraction - leaving Raphael behind, as one Foot Soldier had reported him dead.
Splinter, who was badly wounded in the fight with Shredder, urges Raphael and April to rescue the other Turtles. Together with April's ex-coworker Vern, Raph and April storm Sacks' upstate compound as he is finishing the Mutagen extraction. While Raphael is distracted with fighting Shredder, he takes a helicopter back to his tower in the heart of New York City.
While Shredder works on dispersing the gas and the Turtles attempt to stop him, Vern and April make a move to collect the Mutagen. They find Sacks there, and he fends them off with a gun, also revealing that he killed April's father. He lightly wounds Vern, and April sets off the sprinklers. An injured Vern grabs a microscope and clocks Sacks on the head, knocking him out and he is presumably arrested by NYPD. It is unknown what happens to him afterwards; however, it is possible that he was convicted for his crimes and got a life sentence.
I'm going to be rich. Like, stupid rich.
~ Eric Sacks
You two are adorable. I could just pinch your cheeks!
~ Eric Sacks to Vernon and April O'Neil as he shoots at them.
I understand a girl with dead daddy issues. I do. But you're not gonna stop me!
~ Eric Sacks mocking April O'Neil and her late father while attempting to kill her.
[shoots at April] This is history, repeating itself! Your father walked in on me, April, just like you did!
~ Eric Sacks revealing to April O'Neil that he killed her father as he attempts to shoot her.
It took a few less bullets to take him down, though.
~ Eric Sacks' last words describing how he killed April's father, his lab partner.
Originally, Sacks was going to be a Caucasian incarnation of the Shredder, with his name being an Anglicized version of the Shredder's real name, Oroku Saki. After fan outcries, the studio decided to make the Shredder Japanese, with Sacks being the character's apprentice.
However, Fichtner voices the Shredder in a French trailer of the movie, while Sacks himself is the Shredder in the 3DS video game adaptation. These facts imply that the Shredder's recasting was late in development of the film. Furthermore, since Saki did adopt Sacks, it could be possible that he would have succeded him if Saki passed away or retired.
Sacks and Shredder's plan is similar to Ra's al Ghul and Scarecrow's in Batman Begins, considering both duos aimed to poison a city's water supply. After the plan failed, Fichtner was seen in the next chapter where his bank is being robbed.
It is possible that Sacks survived, as William Fichtner had a three-picture contract for the next two sequels. However, given that the second film bombed at the box office, we might never know what happened to him.
Sacks being born in an American military base is a nod to William Fichtner being born in a New York military base.
Sacks might be in prison, considering that April revealed his involvement with the Foot Clan as well as his murder of his father. That said, because he does not appear in the second film, it is unknown what happended to him.