On 12 February 1881, Cruls was naturalized as a Brazilian citizen by Emperor Dom Pedro II. Cruls took this opportunity to formally change his first name to "Luíz", the Brazilian form of "Louis" or "Luís". A few months later, Cruls's mentor Emmanuel Liais resigned, and Cruls was appointed as interim director of the Imperial Observatory. Liais had become worn down by public accusations of scientific incompetence and dishonesty from Manoel Pereira Reis (an astronomer he had dismissed as head of the Commission of the Empire General Charter in 1878) and returned to Cherbourg, France. However, Pereira Reis was to transfer his animosity to Cruls, and would remain a persistent critic of Cruls and the Observatory for the rest of his life.