Marcus Aemilius Scaurus (c. 163 BC – c. 88 BC, consul of 115, princeps senatus in the same year) is portrayed in Colleen McCullough's First Man in Rome and the subsequent volume in her series both as a stiff-necked patrician, enemy of Gaius Marius, and someone for whom the republic comes first; and who displays a vicious sense of humor.
Basic online information all goes back to a 1911 Encyclopedia Britannica entry.
Plutarch talks about Scaurus briefly in his Moralia, On the Fortune of the Romans.
Mommsen summarizes him thus:
Marcus Aemilius Scaurus
A significant illustration of this is afforded by the chief of the senatorial party at this time, Marcus Aemilius Scaurus. The son of highly aristocratic but not wealthy parents, and thus compelled to make use of his far from mean talents, he raised himself to the consulship (639) and censorship (645), was long the chief of the senate and the political oracle of his order, and immortalized his name not only as an orator and author, but also as the originator of some of the principal public buildings executed in this century. But, if we look at him more closely, his greatly praised achievements amount merely to this much, that, as a general, he gained some cheap village triumphs in the Alps, and, as a statesman, won by his laws about voting and luxury some victories nearly as serious over the revolutionary spirit of the times. His real talent consisted in this, that, while he was quite as accessible and bribable as any other upright senator, he discerned with some cunning the moment when the matter began to be hazardous, and above all by virtue of his superior and venerable appearance acted the part of Fabricius before the public. In a military point of view, no doubt, we find some honourable exceptions of able officers belonging to the highest circles of the aristocracy; but the rule was, that the lords of quality, when they were to assume the command of armies, hastily read up from the Greek military manuals and the Roman annals as much as was required for holding a military conversation, and then, when in the field, acted most wisely by entrusting the real command to an officer of humble lineage but of tried capacity and tried discretion. In fact, if a couple of centuries earlier the senate resembled an assembly of kings, these their successors played not ill the part of princes. But the incapacity of these restored aristocrats was fully equalled by their political and moral worthlessness. If the state of religion, to which we shall revert, did not present a faithful reflection of the wild dissoluteness of this epoch, and if the external history of the period did not exhibit the utter depravity of the Roman nobles as one of its most essential elements, the horrible crimes, which came to light in rapid succession among the highest circles of Rome, would alone suffice to indicate their character.