Alexander Danforth Seyman didn't have the most ideal childhood.  His brother Gregory was eleven years older than him -- a built-in generation gap.  His mother died when he was five years old from lung cancer.  Then, seven years later, his alcoholic deadbeat father split and left Gregory and Xander by themselves.  The brothers were forced to move about the City to affordable housing so they could make ends meet.  Finally, when Xander turned 23, he left to be on his own.

Xander was also a highly skilled nihilist hacker, using the alias Nil Excess ('Nil' from 'nihilism' and 'Excess' from his initials 'XS').  He hacked the NSA database once or twice, but did get caught a few times.  Due to this record, Xander toed a thin line at work, but then he attracted the attention of the Resistance and the Machines in the Real World.  His programming skills were close to Matrix-level.  The Agents, a new version (stronger and faster than their predecessors like Agents Brown, Jones, and Smith) led by Agents Green and Jameson, arranged Xander's firing and tried to co-opt him -- but resembling government-types, they didn't get any sympathy from a professed nihilist like Xander.  Soon after, Morpheus and the crew of the rebuilt Nebuchadnezzar approached him and told him the Truth.  Xander -- or rather, Nil -- was taken out of the Matrix, joining the crew.

Nil's programming skills came in handy when he developed a new type of weaponry for use in the Matrix -- special gloves and boots that generated an electrical shock when used.  During a visit to the Oracle, however, he was given a not-too-cheerful reading that predicted bad times.

Nil ran afoul of Agent Green when he tried to contact his estranged brother, and the evil Agent took control of Gregory's body to try to kill Nil.  The nihilist fought back and inadvertantly killed his own brother in trying to get rid of Agent Green.  Distraught, Nil confronted Agent Green in a motel near an Exit, and used the electrified gloves on Agent Green in a sprinkler-soaked hallway.  The resulting shock distorted the Matrix and destroyed the Agent, but also put Nil in a coma.

Nil later recovered, but the Matrix distortion had caused bits of the Agent's code to lodge in his own code.  This caused him to exhibit Agent-like agility, as well as the ability to pre-empt the Agents' moves, allowing the crew to escape from their grasp.  However, Nil was also linked to the Agents' communication network, which was not designed for human minds.  As a result, painful headaches struck Nil while in the Matrix, and even in the Construct if the Neb was at broadcast depth.  It drove Nil back into a coma, where he confronted Agent Green again and achieved closure when he was able to kill the Agent.

Thanks to the help of his crewmates and a new programmer, Nil recovered and was able to block the Agent-code within him, allowing him to enter the Matrix once again.