Haladki was seen first entering Vaughn's officer shortly after the CIA figured out that Sydney's mother was the one who murdered a dozen CIA agents, one of whom was Vaughn's father. Haladki asked Vaughn if he was interested in dating another agent who was available, but Vaughn declined the offer. (The Box, Part 1) Haladki reported Vaughn because he realized that he was becoming emotionally attached to Sydney. Even when Vaughn went into SD-6 alone during a raid executed by McKenas Cole, Haladki still didn't offer Vaughn any backup and simply tried to explain to his superiors why he should be fired. (The Box, Part 2)
Later, Haladki convinced the DSR not to ignore a warning seen within Page 47 and they later took Sydney into custody after discovering what the prophecy stated. (The Prophecy) Despite their hatred for each other, Vaughn tried to become friends with Haladki, but he refused and continued to pursue his connection with Sydney Bristow. (Q&A) Later, Jack contacted Haladki and forced him to tell him where Sydney was being held. After putting a gun to Haladki's head, he told Jack what he wanted to know.
After finding out that Haladki didn't have clearance for knowing about The Circumference, Jack figured out that not only was Haladki the mole that everyone was looking for, but that he was working for Khasinau, which is why he had been disrupting Vaughn and Sydney's efforts and why he didn't report Vaughn's confirmation that SD-6 had been breached (The Box, Part 2). Jack brutally interrogated Haladki by crushing his hands in a vice and Haladki revealed he had been working with Khasinau for two years. Haladki also told Jack that he needed the Circumference for a battery and that he told Khasinau Sydney was a double agent. Jack, infuriated that Haladki risked his daughter's life, killed him by shooting him in the head. (Almost Thirty Years)
On the Almost Thirty Years audio commentary, the actors and actresses make little jokes about this character and actor.