Wendell was a smart AI attached to the 717th Xeno-Materials Exploitation Battalion during the Battle of Gao in 2553. The 717th battalion was deployed to the planet Gao to retrieve an Ancilla, Intrepid Eye, who had attempted to communicate with the Forerunner ruins on Shaps III after receiving an automated distress signal from them.
After weeks of the 717th playing cat and mouse with the AI, Intrepid Eye killed Ira Halal who was carrying a fragment of Wendell, and subsequently communicated with said fragment. Intrepid was able to place a bug in Wendell's code, without the fragment noticing. This fragment was later retrieved by Fred-104, and reintegrated with the so-called "Wendell Prime".
Wendell had several conversations with Intrepid in the following hours, but foolishly neglected to mention her presence to the SPARTANs. Intrepid was able to "jump" to Fred-104's Mjolnir Armor, from where she later "ate" Wendell, and gained control of several UNSC systems in their make-shift base on Gao.