In Halo: Combat Evolved, the artificial intelligence who assists Master Chief is Cortana.
Cortana is a smart artificial intelligence created by Dr. Catherine Elizabeth Halsey for the United Nations Space Command. She accompanies Master Chief during the game’s events, providing tactical analysis, navigation, translations, and access to computer systems.
The character’s name was inspired by Cortana, the legendary sword associated with Charlemagne in medieval tradition. In the Halo story, Cortana is especially important because she can interact with Forerunner technology and help uncover the secrets of the ringworld installation.
Cortana is sometimes confused with other Halo AIs. Serina is the AI in Halo Wars, while Roland serves aboard the UNSC Infinity. Cortana’s partnership with Master Chief is one of the defining relationships of the original trilogy.