Captain Lock bore many lime green markings on his clone trooper armor, including a lime green stripe down the middle of his helmet, much like the rest of Horn Company. He had a green visor on his helmet and used the standard DC-15S Blaster.
- "But sir, they're commando droids!"
"That does not matter captain, now go."
- ―Lock and Koth while Grievous attacks the Steadfast
Captain Lock was stationed in a corridor on the Steadfast around 21 BBY, with the rest of Horn Company. While in the middle of open space, a Separatist Destroyer. Lock was left to fend off a squad of B2 Super Battle Droids when the Steadfast was tracktored in. After many of the clones accompanying him were shot down, Eeth Koth commanded him to flee to the escape pods with his remaining troops. The captain insisted on staying, stating that commando droids were boarding, but Eeth Koth was not daunted. Obeying Koth's orders, he fled to the escape pods.
After Lock's escape, General Grievous borded, killing many other clones and wounding master Koth. The Steadfast was destroyed after Grievous left with an unconscious Koth. Though it was never clearly stated, Lock presumably survived.
- Grievous Intrigue (First appearance)