A personality component is a part of a Transformer's anatomy that governs their personality and without which they would be a dumb, almost zombie-like mechanoid. Personality components can be removed and replaced safely. Some criminals are imprisoned by storing their personality components in a detention center, where for some reason they resemble energon cubes.
Generation One cartoon continuity
Within this continuity, new personality components can only be generated by Vector Sigma (except, of course, when they're not). Megatron journeyed to Cybertron to grant personality components to the Stunticons. Arriving too late to stop him, Optimus Prime had Vector Sigma imbue sentience within the Aerialbots, thus establishing a precedent that would not always be followed in the animated series.
However, in keeping with this trend Starscream lacked access to Vector Sigma in his attempt at forming his own army to overthrow Megatron. Therefore, he traveled to Cybertron where he liberated the already-formed personality components of the Renegade Decepticons.
After selling his fellow Combaticon parts, Swindle had a bomb placed in his head and was ordered by Megatron to reassemble his comrades or be destroyed within 15 hours. Swindle managed to get all the Combaticon parts except Brawl's personality component. He didn't think it would matter and was disappointed to find that they could not merge into Bruticus. Megatron was not amused.