Leo and Irene
Leo the Isaurian (ca. 720 AD,
Louvre museum, Paris)
When Justinian's assassin Philippicus turned out to be a worthless party animal, he was killed, and in 713 AD the people of Constantinople chose a court official named Anastasius II to be the next emperor. Anastasius (ann-ah-STAYS-yus) was a practical guy, with good ideas - but in 715 AD the army rebelled and deposed him anyhow. One of the leading generals, who had risen from the peasantry, Leo the Isaurian, took over. Leo was an ambitious and successful man, who had been planning his take-over for some time. He was just in time to save Constantinople from another Arab siege in 717. The Bulgars marched down from the north and helped out. But despite this great success, Leo is best remembered for having introduced iconoclasm to the Roman Empire (so it's pretty ironic that we have a good image of him!).
When Leo died in 741, his son Constantine V succeeded him, and continued his iconoclastic policies. He also made efforts to shut down or reduce the monasteries, both because they were hiding icons, and because a plague in 745-7 killed a lot of people and so more children were desperately needed and monks didn't have children.
Constantine V was also a good soldier. He didn't have to fight the Arabs, because under the Abbasids the Arabs were no longer so interested in conquering the Roman Empire. He showed little interest in defending Italy from the Lombards, who invaded in 751. But he fought the Bulgars year after year, until he died in 775 at 57 years old.
Constantine's son Leo IV succeeded him, but Leo IV died in 780, leaving a 10 year old son, Constantine VI, to succeed him. The boy's mother, Irene, took over as regent for her son. Irene was originally from Athens, and she was a total iconodule: she loved images and as soon as she came to power, she put all the images back. In this way she also temporarily mended her relationship with the Pope in Rome. But when Constantine grew up, Irene refused to hand over power to him, and instead put him in prison. Even when Constantine was rescued and put in power, in 792 he ended up letting his mother have the power again. In 795 she had him killed, and from then on, since Constantine left no son, Irene ruled not as regent but as Emperor, the first woman to do so.
In 800 AD, however, Charlemagne had himself crowned Holy Roman Emperor in Rome, challenging Irene, and in 802 he made matters worse by sending her a proposal of marriage. Irene seemed to be about to accept the proposal, when her horrified subjects deposed her and exiled her to Lesbos, where she died the next year.