|Ascending to the throne of Russia at the age of 3, following the demise of his father, Ivan did not actually rule until 1547. He styled himself "tsar", the first Russian ruler to do so. One of Ivan's most important moves was to try and curtail the traditional power of the senior nobility and expand the influence of the minor aristocracy. Though Ivan promoted legislative and church reform for the better part of a decade, an incipient boyar rebellion led to Ivan's becoming quite ruthless. Arrests and executions marked Ivan's middle years. He fought the Tartars and other foes, eventually extending his control to Kazan, Astrakhan, Narva, among other areas. Towards the end of his reign, Ivan appeared to soften somewhat, according posthumous pardons to some of his earlier victims. But the old Ivan had not completely mellowed: during an episode of rage in 1581, Ivan killed his heir, which led to his being succeeded by Fedor, his weak and probably feeble-minded second son.