Micipsa was the third son of king Massinissa of the Massylian (eastern) Numidians. When this king died in the spring of 148 BCE,note[Livy, Periochae 50.7.] the Roman officer Publius Cornelius Scipio Aemilianus acted as the executor of his will.
To Micipsa, the oldest, a lover of peace, he assigned the city of Cirta and the royal palace there. Gulussa, a man of warlike parts and the next in age, he made the director of matters relating to peace and war. Mastanabal, the youngest, who was learned in the law, was appointed judge to decide causes between their subjects.note[Appian, Punic Wars 106.]
This took place during the Third Punic War, which did not start very well for the Romans. Their enemies, the Carthaginians, made attempts to lure Numidians to their side, including Mastanabal. However, this attempt failed.note[Appian, Punic Wars 111.]
Micipsa's two co-rulers succumbed to an illness quite early,note[Sallust, Jugurtha 5.6.] so we do not know much about Gulussa and Mastanabal. He had two sons: Gauda and the future king of Numidia, Jugurtha.note[Sallust, Jugurtha 5.7.]