Historically the church understood that the first seal, the white horse of righteousness, with a rider exercising military might and ruling authority, who went out to conquer, and who did increase politically and territorially, was fulfilled from 96-180 ad by the five righteous emperors of Rome. (The First Four Seals: 96-300 AD, pg. 24.)

For the Scriptural interpretation of the colors and symbols of the first four seals, as traditionally understood by the church, there is no better source than Albert Barnes, who employs minute detail in his explanation of each symbol, in Notes on the New Testament … : Revelation, pp. 132-158.

“The wicked Domitian was succeeded by Nerva, a good, wise, and generous old man, who did all he could to repair the wrong which Domitian had done, and to induce the Romans to lead better lives.”

H. A. Guerber, The Story of the Romans, pg. 239.

“Such was the respect that the Romans felt for Trajan that during the next two hundred years the senators always addressed a new emperor by saying: ‘Reign fortunately as Augustus, virtuously as Trajan!’ Thus, you see, the memory of a man’s good deeds is very lasting; even now Trajan’s name is honored, and people still praise him for the good he did while he was emperor of Rome.”

H. A. Guerber, The Story of the Romans, pg. 242.

“Trajan was succeeded by his cousin Hadrian, a good and true man … and his next [act as emperor was] to pardon all who had ever injured him. Thus, we are told that on meeting an enemy he said: ‘My good friend, you have escaped, for I am made emperor.’

“Hadrian was very affable, and always ready to serve others. When asked why he, an emperor, troubled himself thus about others, he replied: ‘I have been made emperor for the benefit of mankind and not for my own good.'”

H. A. Guerber, The Story of the Romans, pg. 243.

“[Trajan] is the second of the Five Good Emperors, the first being Nerva.”

“Ancient Rome,” Wikipedia.

“Nevertheless, the ability and enlightened statesmanship of Marcus Aurelius are undoubted. Indeed, they were only equaled by the purity and beauty of his personal life. He regarded his exalted office as a sacred trust to which he must be true, in spite of the fact that he would have greatly preferred to devote himself to reading, study, and philosophy, which he deeply loved. … he found time to record his thoughts and leave to the world a little volume of meditations written in Greek. As the aspirations of a gentle and chivalrous heart toward pure and noble living, these meditations are among the most precious legacies of the past. Marcus Aurelius was the last of a noble succession, the finest spirit among all the Roman emperors, and there was never another like him on the imperial throne.”

James Breasted, Ancient Times: A History of the Early World, p. 665.