The optimates ("Best Men," singular optimas; also known as boni, "Good Men") were the traditionalist majority of the late Roman Republic. They wished to limit the power of the popular assemblies and the Tribune of the Plebs, and to extend the power of the Senate, which was viewed as more dedicated to the interests of the aristocrats who held the reins of power. In particular, they were concerned with the rise of individual generals who, backed by the tribunate, the assemblies and their own soldiers, could shift power from the Senate and aristocracy. They were opposed by the populares.
Many members of this faction were so classified because they used the backing of the aristocracy and the senate to achieve personal goals, not necessarily because they favored the aristocracy over the lower classes. Similarly, the populares did not necessarily champion the lower classes, but often used their support to achieve personal goals.