Commander Bruce Maddox was a 24th century Starfleet cyberneticist, and the Associate Chair of Robotics at the Daystrom Technological Institute. He was the only person to object to Data's entry into Starfleet Academy in 2341 on the grounds that, as an android, Data did not qualify as a sentient being.
In 2365, Maddox earned Admiral Nakamura's support on a proposal to disassemble and reverse-engineer Lieutenant Commander Data for research. Having studied the works of Doctor Noonian Soong, Maddox believed the untested procedure would provide him with the final knowledge required to allow for mass production of Soong-type androids. After presenting his proposal to Captain Jean-Luc Picard, Commander William T. Riker and Data, Data studied Maddox' proposal and found it to be flawed in its ability to preserve the nuances of his positronic brain, prompting Maddox to assert his authority and order Data to submit by transferring him from USS Enterprise-D to Maddox' command aboard Starbase 173.
Data refused and resigned from Starfleet, but Maddox challenged his right to do so, claiming that Data was property, not a sentient lifeform, a position initially supported by Captain Phillipa Louvois of the Judge Advocate General's office. Captain Picard challenged this position, stating that Data is arguably a sentient being as defined by most of Maddox' own criteria. Furthermore, Data currently represented an entire race and duplicating him for the purposes of forced labor constituted slavery. Louvois agreed with Picard's standpoint and ruled that Data was a sentient being with full rights under Federation law. Data nonetheless encouraged Maddox to continue his research. (TNG: "The Measure Of A Man")
When Data's program was infiltrated after an Iconian software transmission his systems went down. Geordi La Forge mentioned that an expert such as Maddox, or somebody similar could help. (TNG: "Contagion")
Despite the troubles inherent in their earlier relationship, Data held no ill will against Maddox, and corresponded regularly with him, keeping detailed records of all inter-personal activities. (TNG: "Data's Day")
In Articles of the Federation, Maddox, now a captain, argues before Federation President Nan Bacco and the Federation Judiciary Council that B-4 should not be disassembled. He was successful in his arguments against Doctor Lars Patek, and B-4 remained in the custody of Maddox and the Daystrom Institute.