Irina believed Chekov to have been too rigid and Chekov believed Irina to have been too free-spirited. The two had several disagreements before they parted ways, each accusing one of leaving the other. When Irina dropped out of the Academy, Chekov left, but came back to look for her, who was at the time staying in the city with friends. Irina eventually joined the counterculture movement of Dr. Sevrin and his search for the mythical planet Eden, while Chekov joined the crew of the USS Enterprise.
In 2269, Galliulin, Dr. Sevrin, and four of their colleagues stole the space cruiser Aurora to further their search for Eden, but they were apprehended near the Romulan Neutral Zone by the Enterprise on stardate 5832.3.
During the return trip to a Federation starbase, Galliulin encountered her lost love, the now-ensign Chekov. Initially happy to see one another, Chekov adamantly disapproved of her new lifestyle and attempted to cast her off. Galliulin was coerced by Sevrin to help him commandeer the Enterprise. She visited Chekov, who, on assignment to help Spock locate Eden, was working in auxiliary control, to apologize for upsetting him. Her ulterior motive, however, was to subtly use him to gain knowledge of the systems of the starship, which was later used by Sevrin for hijacking control of the Enterprise.
Galliulin aided Sevrin in disabling the ship's crew and appropriating the Enterprise shuttlecraft Galileo II, which they used to get to the planet. However, on the planet's surface, they discovered that their "Eden" was actually a poisonous planet, and her feet were burned on the acidic grass. Galliulin and three of the surviving followers were transported back to the Enterprise, where they were let off at their previous destination, the nearest starbase. (TOS: "The Way to Eden")
Irina Galliulin was played by actress Mary-Linda Rapelye.
Her role was originally written as that of Joanna McCoy for the episode's original title "Joanna". However, when it was heavily rewritten, the part, as well as the episode, were both renamed by the final edit.
In the novelization of Star Trek VI: The Undiscovered Country, Chekov reflected to himself, while the Enterprise was on the way to confront General Chang over Camp Khitomer, that Irina has finally ended their relationship.
In Star Trek II: Biographies, her name was misspelled "Irini".
Irina Galliulin (β)'s alternate reality counterpart served aboard USS Enterprise as a sciences division officer. She takes an interest in Pavel Chekov when she catches him dreamily stargazing in "Behemoth, Part 1", promising to help him pronounce his "v"s.