Bill Steele was an FBI ASAC (Assistant Special Agent in Charge) who worked with the team when an allegedly bomb-bearing tractor driven by a down-on-his-luck farmer named Harold Clark was parked outside the Institute. In reality, this was a ruse designed to distract law enforcement from another bomb planted by domestic terrorist Ron Jackson. During the mission, Steele and Lightman butted heads over procedure.
We are given no biographical information about Steele in the televised account based on these events. However, my research has uncovered evidence that Steele was born in a small town in California around 1957. His mother was a local woman whose friend was murdered by a man who was wanted in several states (unfortunately, my records are vague as to who this may have been. Patient research continues). An FBI agent came to town, and during the investigation, an attraction sprang up between Ms. Steele and this agent, despite the latter having been married for a year and having a baby son back in Philadelphia. They had a brief torrid affair, and Bill was born nine months later. Never knowing his father personally, he at least came to know his name and occupation, and followed in his footsteps by joining the Federal Bureau of Investigation.
Once the case closed, the agent returned to Philly and his wife and son. His wife never knew of the agent's affair, but the son learned of it after, like his half-brother, honoring his father by joining the Bureau, showing special expertise in forensics. Anger at his father's infidelity engendered in Albert Rosenfield a deep dislike of small towns and the people inhabiting them.
This aversion boiled over when Albert was sent to Twin Peaks, WA to assist his good friend and fellow Special Agent Dale Cooper by conducting tests on the body of 17-year-old Laura Palmer. Albert repeatedly treated the authorities and inhabitants of Twin Peaks with contempt, ultimately leading to Sheriff Harry S. Truman punching him in the face. Despite this, Albert revealed on a subsequent visit that despite his gruff, hostile tone he was at heart a pacifist, and during further trips to Twin Peaks he made his peace with Truman, if not the other natives. It is unknown whether Albert Rosenfield and Bill Steele ever met, but if so, I seriously doubt the meeting was cordial on Albert's part.
Lie to Me - television series, particularly the episode "Tractor Man"
Twin Peaks - television series
Twin Peaks: Fire Walk with Me - film
Twin Peaks Star Pics Cards - Trading cards, particularly #63, "Agent Rosenfield"