It’s hard to identify a single aspect of the umma left unchanged by al Ma’mun’s long reign: he had a major impact politically, socially, intellectually, religiously, and beyond. Despite its many impressive achievements however, its flaws receive an inordinate amount of attention in our sources. Even when describing al Ma’mun’s successes, narrations employ more of a wistful tone than a triumphant one. Attitude notwithstanding, al Ma’mun is still a strong candidate for best caliph, and even his detractors don’t venture to challenge his significance.