In 1987, TSR published Top Secret/S.I. ("Special Intelligence"), a revised edition designed by Douglas Niles. S.I. introduced a more structured gaming environment in which players worked as agents for secret intelligence agency ORION against its evil adversary, WEB. Later source books in the product line introduce both supernatural (Agent 13) and futuristic (F.R.E.E.Lancers) adventure settings. These settings introduced several recurring characters such as Sebastian Cord and Agent 13.
Top Secret/S.I. uses a fast, simple combat system based on percentages. With as little as a single die roll, a player can know not only if a character was hit, but what part of the body was hit and the extent of damage.
Based on a character's stats, skills, bonuses and penalties, the gamemaster (Administrator) gives that character a certain percentage chance of hitting a given target. The player then rolls percentile dice; a result that is equal to or lower than the to-hit percentage succeeds. The hit location is determined by the 'ones' digit of the same roll, and hand-to-hand combat damage is determined by the 'tens' digit. Weapon damage ignores the 'tens' of the first roll, and requires a second roll based on the weapon's characteristics.
Character sheets in Top Secret/S.I. resemble agent dossiers, and are intended to provide quick and easy reference to all a player's stats and skills. They also provide a detailed map of the ten possible hit spots of a character's body, and a blank portrait area for drawing or attaching a depiction of the character.
Source: Wikipedia, "Top Secret/S.I. edition", available under the CC-BY-SA License.