Who was the byzantine emperor that launched iconoclasm in the 700s?

The "First Iconoclasm", as it is sometimes called, lasted between about 726 and 787. The "Second Iconoclasm" was between 814 and 842. According to the traditional view, Byzantine Iconoclasm was started by a ban on religious images by Emperor Leo III and continued under his successors. It was accompanied by widespread destruction of images and persecution of supporters of the veneration of images. The Western church remained firmly in support of the use of images throughout the period, and the whole episode widened the growing divergence between the Eastern and Western traditions in what was still a unified church, as well as facilitating the reduction or removal of Byzantine political control over parts of Italy.