Along with SHODAN herself, William Bedford Diego is one of the few characters in System Shock 2 who has explicit ties to the original System Shock, as he was a direct descendant of the duplicitous TriOptimum executive Edward Diego, whose greed and self-interest directly precipitated the disastrous Citadel Station incident. However, rather than being vilified by association for the heinous crimes of his father, which resulted in innumerable deaths, Diego was successfully able to step out from under his father's shadow in order to become a well-respected member of society. Pursuing a career in the military, Diego was lauded for his actions during the Battle of Boston Harbor, though it is not stated during the game what he did to earn such esteem or what the nature of this conflict was. Regardless of the means, Diego clearly proved his worth in the eyes of his peers, and as such was chosen to be the captain of the UNN Rickenbacker, the escort vessel accompanying the world's first faster-than-light starship, the Von Braun, on its maiden voyage.
Despite his many accomplishments and wide public acceptance, it is also implied that Diego was still haunted by the deeds of his father, and may in part have chosen the life of a soldier in order to distance himself from Edward Diego's shady private-sector persona. He was deeply mistrustful of corporate culture in general as evidenced by his antagonistic relationship with Anatoly Korenchkin, the captain of the Von Braun, whom he held in low regard. He was also resentful of any assumptions that the apple may not have fallen far from the tree, going as far as to say to Korenchkin on one occasion that "just because my father swam with the sharks doesn't mean that I do." As a military man, Diego was shown to take his responsibilities as captain very seriously, even after experiencing the chaotic deterioration of the Von Braun and the seductive influence of the Many, and he took full ownership of his own part in the mission's failure.
System Shock 2
Though the player character in System Shock 2 is a soldier assigned to the UNN Rickenbacker, and is presumably under the direct command of Captain Diego, the player has little direct interaction with him throughout most of the game. It is learned through audio logs that Diego fell under the influence of the Many not long after first contact on Tau Ceti V, though later on it comes to light that he was able to achieve awareness of his compromised state long enough to forcibly remove the annelid worm from his body, thereby regaining his free will. He is severely weakened in the process, however, and after performing self-surgery he directs the player to find him in the Rickenbacker's sickbay largely because he is in no position to leave. He tells the player that he is in a unique position to help, being that he is capable of seeing the situation "from every imaginable perspective," though he unfortunately dies before the player can reach him. The exact cause of his death is unclear, and in his final audio message he warns the player that they cannot trust anyone.