Reza Pahlavi, who as a boy was groomed to be the next shah of imperial Iran but has spent nearly five decades in exile, has emerged as a rallying figure in the protests shaking the Islamic Republic. The chant of “Pahlavi will come back!” has become a mantra for many of the protesters, while the US-based 65-year-old has urged nightly actions in video messages. Pahlavi’s prominence in the protest movement has surprised some observers. Pahlavi has during the latest protest wave shown an “ability to...