En route to the starbase, the Enterprise stopped at Gamma Hydra IV, where Captain James T. Kirk and the other senior officers were infected with a radiation disease that caused premature aging. This forced Stocker to assume command of the Enterprise.
As acting captain, Stocker violated the Romulan Neutral Zone, in an attempt to take a shorter route to Starbase 10 in the hopes of reaching the base, and its "superior" facilities, in time to save the afflicted officers. This led to an attack on the Enterprise by several Romulan Birds-of-Prey. Being an inexperienced officer in battlefield conditions, Stocker panicked and almost lost the Enterprise before the cured Kirk could retake command and save the ship, using a broken code to deliver a false message warning Starfleet ships to avoid the area after he detonated a corbomite device (by the time the Romulans realized they had been fooled, the Enterprise was safely back in Federation space).
Kirk knew that he had been in no shape for duty and held no ill will toward Stocker, though Kirk did insist that there was little a starbase could do that a ship could not – which the commodore admitted he was now well aware of, assuming the right person was in command. (TOS: "The Deadly Years")
His assumption of command aboard the Enterprise eventually became a precedent listed in the Federation Judicial Code. In 2376, Kathryn Janeway came across Stocker's actions during her research into precedents which might let The Doctor, a hologram, assume command of USS Voyager. (VOY: "Tinker Tenor Doctor Spy", okudagram)
Stocker was played by actor Charles Drake.
The script of the episode gave Stocker's first name as "George".
The following was said of Stocker in the stage directions from the final draft script of "The Deadly Years": "Commodore George Stocker, in his mid-forties, with the look of an able administrator (which he is)."
In the cast portion of the script, Stocker was described as being somewhat younger, in his "late thirties," though that section of the teleplay also characterized him as "an administrator."