Who are the Saudi nationalists? The growing body of social science research on mis- and disinformation campaigns in autocratic states emphasizes manipulative state strategies and bot armies. And while repressive regimes and state-led bot accounts are certainly relevant, this research focus misses the important role that bottom-up pro-regime movements can play to defend and authenticate autocratic regimes, particularly in episodes of autocratic change and renewal. This chapter uses the Saudi nationalist pro-regime movement (the Watanjiyya) that defends the Saudi nation, state, and monarchy on Twitter and attacks any critical voice as case-study to explain the existence of bottom-up pro-regime activism. The chapter draws on more than 90 original interviews with Saudi nationalists that I conducted across the kingdom between November 2021 and May 2022, previously disregarded data from Saudi online forums from the early 2010s and data from the Saudi Twitter sphere. First, the chapter finds that the Watanjiyya emerged as a bottom-up reaction to labour market pressures in the late 2000s and particularly to geo-political and (perceived) identity threats during the the Arab Spring (2011), pre-dating the state-led national identity project under Prince Mohammed bin Salman since 2015 by many years. This demonstrates that the Watanjiyya are not just attached to MBS or are a mere result of his policies. Second, the chapter shows that the Watanjiyya are motivated by the belief in the legitimacy of the regime, instead of receiving material benefits of some kind, developing into a crucial pillar of Saudi regime stability. The chapter highlights the relevance of bottom-up movements for the stability of autocratic regimes beyond mere state strategy.