Stuart Radzinsky was a member of the DHARMA Initiative who worked at the Flame station in 1977 as Head of Research, enjoying a relatively high leadership position within the Initiative. Radzinsky worked alongside Dr. Pierre Chang at the construction site for the Swan. He is described as having a photographic memory. Many years later, he became Kelvin Inman's partner inside the Swan, the same location where, according to Inman, he committed suicide.
On the Island
Radzinsky argues with Sawyer and Jin over the handling of their prisoner. ("Namaste")
Radzinsky was first seen working at the Flame station, building a model of the Swan station. He was visited by Jin, who wanted to know if a plane had crashed on the Island. After Jin physically intimidated him, Radzinsky contacted the other stations to ask if anyone had seen a plane. All stations answered negatively, but Radzinsky was suddenly alerted to an intruder who tripped a motion sensor. He followed Jin and found the intruder, presuming him to be a hostile, unaware that Jin knew the man. After Sawyer came to the Flame, where they held the intruder captive, Radzinsky asserted that he was a spy, that he had seen the model of the Swan and perhaps other critical information, and that they should kill him. Sawyer took the prisoner away over Radzinsky's objections, who stated that he would take the matter directly to Horace. Radzinsky then traveled in the DHARMA van with Sawyer, Jin, and Sayid to the Barracks, where Jack, Kate, and Hurley were shocked to see Sayid held captive. ("Namaste")
Radzinsky and Phil look on as Oldham interrogates Sayid. ("He's Our You")
Later, Radzinsky was present while Oldham gave Sayid truth serum, and became extremely paranoid regarding Sayid's knowledge of The Swan. Radzinsky was present during "the vote" on whether to keep Sayid alive. He was the group's biggest supporter of Sayid's execution, and his motion was agreed upon unanimously, with Sawyer being the most reluctant. ("He's Our You")
Horace later sent Miles to take a "package" to Radzinsky, who would give him something back in return. Miles drove to Grid 334 in hostile territory, where he was stopped at gunpoint by Radzinsky. Miles gave him the package, which contained a body bag to put a dead DHARMA worker in. When Miles enquired as to what had happened, Radzinsky said the man fell in a ditch and told Miles to leave with the body. Miles later brought Pierre Chang to meet with Radzinsky at the secret Swan construction site. ("Some Like It Hoth")
An injured Radzinsky arrives at the Barracks after his shoot-out with Jack, Kate and Faraday. ("The Variable")
Radzinsky and two other DHARMA members went to the motor pool, where Jack, Kate, and Daniel were arming themselves. When Radzinsky saw their weapons, he accused Daniel of lying about the group's intentions, and a firefight ensues when Daniel tried to make a getaway. Daniel was grazed in the neck by a bullet, and Radzinsky was shot in the arm. As Jack, Kate, and Daniel made their way to the jeep, Jack opened fire on a fuel tank, causing a tremendous explosion. They escaped as the dust settles, and Radzinsky called for someone to "sound the alarm." Immediately Radzinsky set off for Sawyer's house. When he entered the house he yelled at Sawyer about why he wasn't outside dealing with the situation. Sawyer asked him what happened and Radzisnky told him that he'd been shot by a physicist, and the new recruits. They then heard a noise, to which Sawyer said someone must be outside, Radzinsky headed down the hall, and when he heard noises coming from the closet he opened it and found Phil. He then immediately pointed his gun at Sawyer and Juliet, and told them to get on the ground. ("The Variable")
Radzinsky asserts his command over Horace ("Follow the Leader")
From there, Radzinsky took them to the Security office. He, along with Phil, interrogated them to the to the displeasure of Horace who had tried to stop them, but Radzinsky told him that he was no longer in charge if he couldn't do what needed to be done to protect their work. Radzinsky threatened to kill them if they didn't tell him where Kate was, but Sawyer refused to tell. Pierre Chang later interrupted them, and told them to evacuate all non-essential personnel from the Island, because of what will happen at the Swan site. Radzinsky refused and told Pierre that he was in charge, after Pierre tried to get Horace to comply. Sawyer interrupted and told them that he would comply if he saved the women and children, and put him and Juliet on the sub. Radzinsky agreed, and gave him a notebook to draw a location to The Others' camp. ("Follow the Leader")
Radzinsky arrives at the Swan site. ("The Incident, Part 1")
During the time when Sawyer, Juliet, and Kate were planning to stop Jack from detonating the bomb Radzinsky returned to the Swan's construction site to continue drilling into the electromagnetic pocket. When he arrived at the site, Dr. Pierre Chang was already there and had stopped the drill due to the possibility of the drill bit melting. Radzinsky turned the drill back on, telling Chang that they had enough water to cool the drill down. Radzinsky then said that he had been designing and planning The Swan for six years, and that when the station was completed, they would be manipulating some of the most powerful electromagnetism in the world. Chang criticized Radzinsky, telling him that this wasn't an ideal time for experiments, citing the potentially cataclysmic events that could occur if they drill into the magnetism and a possible insurrection. Radzinsky snapped that "if Edison had been afraid of the consequences we'd still be sitting in the dark," and continued the drilling procedure. Shortly after this he received a radio call from Phil stating that the prisoner from before had returned and that a firefight had ensued. Radzinsky ordered him to immediately bring backup to the construction site to protect it from Jack and his team. "The Incident, Part 1"
Radzinsky attempts to flee the Swan site by Jeep. ("The Incident, Part 2")
Phil arrived not long after he was instructed to with a small team of men and was told by Radzinsky to set up a perimeter. When one of the men positioned around the site caught a glimpse of Jack he took a shot, and a large gun fight took place. Hearing the commotion, Kate, Miles, Sawyer, and Juliet rode in on a DHARMA Van and aided Jack in the fight. Throughout the course of the encounter Sawyer made his way behind Phil and Radzinsky, knocking down Radzinsky and holding Phil at gunpoint. At this point (with the survivors in a place of power) Jack made his way to the hole and dropped the core of the bomb down it. When the electromagnetism began pulling things into the hole, Radzinsky and two men tried to make an escape in a DHARMA jeep, which was then flipped by the strong pull of the electromagnetism. It is unknown how Radzinsky survived the Incident and possible hydrogen bomb blast. ("The Incident, Part 2")
Radzinsky's blood stain in the Swan ("Live Together, Die Alone")
At a later time, Radzinsky moved to the completed Swan station, where he worked with Kelvin Inman. Radzinsky was the originator of the blast door map, which he worked on with laundry detergent, a paint brush, and the aid of his photographic memory. He was able to fake a lockdown incident (having had a part in designing the station, he knew its workings intimately) making it possible to work on the map more deliberately. Radzinsky also edited the Swan Orientation film for unknown reasons, and placed the edited portions within a Bible in the Arrow station. His erratic behavior and subsequent suicide may suggest an eventual mental breakdown. ("The Other 48 Days") ("What Kate Did") ("Lockdown")
Kelvin explained to Desmond that, while he was asleep, Radzinsky committed suicide by putting a shotgun in his mouth and firing it, creating a blood stain on the ceiling. Radzinsky's remains were later buried in the jungle outside the Swan station entrance. Because of the Swan station protocol, Kelvin had to bury him within 108 minutes. ("Live Together, Die Alone, Part 1")
When Walt's rescue party reached the capsule dump, Kate found a notebook in which a particular entry mentions the activities of "S.R.", who was apparently a resident in the Swan station and was surreptitiously monitored from the Pearl station by the note taker. As the Pearl's function likely ceased with the Purge (given the staff there worked in eight hour shifts), it can be concluded that Radzinsky took up residence well before this time.
- Zuleikha Robinson once accidentally referred to her character as Ilana Radzinsky in an interview. Ilana's actual surname is Verdansky.
- This method of suicide was also used by Sam Toomey.
- "Stuart" is the French form of "Stewart," meaning "steward" or "guardian." Stuart would have been the guardian of the Swan before his death.
- Radzinsky's death was confirmed by script coordinator Gregg Nations  and by Carlton Cuse and Damon Lindelof on Access: Granted from the Blu-ray Disc release of Lost: The Complete Third Season .
- In Access: Granted, the producers jokingly mention a possible Lost spin-off show called "Radzinsky's Travels". It would involve Radzinsky exploring the island and creating the Blast Door Map.
- In the video game Lost: Via Domus, Radzinsky's journal can be found. It discusses the blast door map and the Incident Room. ("Forty-Two")
- In addition, photographing the bloodstain on the ceiling will unlock the "Radzinsky" achievement on the Xbox 360 version.
- In the casting call Radzinsky is described as: "Marty Jankowsky-40s to 50s, Caucasian, very smart and controlling. Marty has his own way of doing things and god help you if you cross him and/or try to alter his very precise process. A deep and free thinker he uses his fierce intellect as a weapon." 
- Eric Lange, the actor who plays Radzinsky, said in an interview with TV Guide that Radzinsky's job as Head of Research makes him "second-in-command" of DHARMA.
- Radzinsky's death would have taken place between 1991 and 2001. Kelvin Inman joined DHARMA between 1991 and December of 1992 (the purge) where he would become Radzinsky's partner. When Desmond arrives on the island in 2001, Radzinsky is already dead.
- Radzinsky most likely died fairly recent to Desmonds arival to the Swan, due to Kelvin's condition. Kelvin appeared relatively healthy, for a man possibly sleeping for 2 hours at a time. Judging by Radzinsky's attitude for the Swan station the Station appeared more maintained back in 2001 than in 2004.
- Out all of the main characters, Radzinsky has met Jack, Juliet, Ben, Sawyer, Miles, Sayid, Kate, Daniel, Hurley and Jin.
- For fan theories about these unanswered questions, see: Stuart Radzinsky/Theories
- When did he come to be stationed at the Swan?
- Why did he edit the Swan video?
- Why did he create the blast door map?
- Why were so many of the well-known DHARMA Stations missing from the map?
- What drove him to commit suicide?