A highly learned jurist who is capable of Ijtihad, i.e., reasoning about the law through applying complex methods and principles of interpretation. Mujtahids are of various ranks, the highest of which is reserved for the one who is said to have fashioned the very methods and principles that he and others in his school apply, while those who are loyal to, and capable of applying, these principles belong to lower ranks.

Source: Hallaq, Wael B., An Introduction To Islamic Law, 1st edn (New York, USA: Cambridge University Press, 2009), p. 175