Lincoln James Potter (alias Nick Stackhouse and Gabe Marcel) is the Assistant U.S. Attorney investigating the Sons of Anarchy Motorcycle Club. He is ruthless and determined, willing to cross legal boundaries to get a job done. Although he can be viewed as the main antagonist of Season 4 overall, he also performs acts that are beneficial to both the Sons and Charming, and thus he can also be viewed as an anti-hero of sorts.
Lincoln was an extremely calculating and strategic individual, hiding his cunning behind a mask of being an eccentric. Despite his oddness, he had an outgoing, friendly, and calming demeanor. While conducting business with criminals, he'd put on an emotionless and passive attitude, never allowing himself to seem visibly frustrated even when his best laid plans were ruined by the CIA. Almost always being caught up in his own thoughts of making plans, he would often do strange things that seemed to help him brainstorm such as drinking chocolate milk, hum songs to himself, and smoke cigarettes, even smoking one while reclined upside down in a chair as he contemplated his strategy. He was also very organized, creating a war room with very detailed plans taped all over its walls that included; pictures of his targets, countless sticky notes, and timelines.
His appearance was incredibly unique for an Assistant US Attorney, sporting long hair and a beard and almost always wearing his brown leather jacket, making him look very reminiscent of a man from the 70's as well as ironically, a biker, which he was, having owned a motorcycle of his own.
Shortly before the group of Sons were released from prison, Potter arrived in Charming and with his task force that included members from both the ATF and the FBI, setting their sights on bringing down the entirety of the Sons of Anarchy, RIRA, and the ROC in one swift move. Potter rented space on the third floor at the Sheriff's Department, putting together his "war room" which contained all of their collected information on the gun running connection, including pictures of all members and associates involved with the illegal operations. On the day of Clay Morrow and the other captive SOA members' release, Potter saw them arrive in Charming after buying a pack of cigarettes, driving past them on his own bike and giving them a nod as he passed after they had been blockaded by Sheriff Roosevelt. Later, he visited the sheriff, informing him of who he was and that he was interested in working with him. He brought Roosevelt to the war room and laid out their plans, recruiting him into their top secret task force. Potter explained that they'd be able to attack soon due to a planted mole in the ROC but after the Sons killed the Russians in retaliation for bad blood between them, Potter had to put this plan on hold, deciding to tread water after realizing that there was a whole other player involved with all of this; the Galindo Cartel.
He then checked on the members of SAMCRO and found a potential use for Juice, who had concealed his African-American father from the club, since the MC doesn't allow blacks in the club. Potter used this information to blackmail Juice through Roosevelt, turning Juice into a rat. Potter would also play another underhanded tactic with Otto, by giving him accurate information on Luann's autopsy that revealed that Bobby had sex with her prior to her death. Potter tried to convince Otto into betraying the club, using the autopsy information to make Otto believe Bobby killed Luann.
Completelly unrelated to his case was that he met with Gemma on Roosevelt's wife flower shop under a fake name, and revealed to her that Jacob Hale's protect of Charming Heights was in danger of a time limit if he could not find investment after the Russian bodies were dumped on one of his construction sites, which left him with a huge financial hole. Thus hinting he wanted the Sons to destroy Hale's plan. Also in this scene is a very cryptic line from Gemma as Potter is lighting her cigarette, "Do I know you?"
Roosevelt would take Juice to talk with him on the pretend that it was to check him on his weed shop. Potter would force Juice into securing some proof of the club's involvement with the cartel, and Juice robbed a brick of cocaine (that got Miles a new patch, killed and framed for the theft). Roosevelt confronted Potter in that Juice would be killed if he was discovered, but he did not care as Juice would nonetheless act on their favor with both the fear of being kicked out or killed. This plan did not work and Juice feeling guilty would attempt suicide, which prompted Roosevelt to tell Potter that Juice could no longer be used as he was serious.
Potter then proceeded to use a more drastic tactic centered around Otto. Potter was well aware of the meeting he had with Bobby in which Bobby apologized and promised Otto that they had killed Georgie Caruso, Luann's potential murdered and had it recorded. Then he investigated and revealed to Otto, photos that proved Caruso was still alive which was enough for Otto to side with Potter after feeling betrayed. Potter decided to show himself and his war room to Juice and all the intel that they had on SAMCRO and the RIRA that could be used on a RICO case that could potentially arrest the whole every charter of the Sons of Anarchy, and thus forced Juice to cooperate with them regarding the meeting with but the Irish Kings and Galindo Cartel members, and giving them information, assuring him that if he worked his role fine, he would exclude the Sons of Anarchy from the RICO act, and with little choice Juice accepted. Upon seeing the great lengths that Potter was willing to go and the underhanded tactics he employed, he slowly began to grow disgusted at Potter and distance himself from him. Potter had all he needed on his hands as Otto had signed all the papers that confirmed his participation and that of Bobby's on criminal activities, and by default, the club's. Prior to agreeing, Otto has Potter agree with 3 conditions. That Lenny "The Pimp" is allowed visitations, that his own execution date is carried before schedule, and that he allows a face to face with Bobby. Potter agrees to all of them and eventually allows the two to meet, and is witness to when Otto confesses he ratted on the club and when Bobby is taken into custody.
Eventually the day of the meeting came, and Potter was ready with a large team of Law Enforcement on a camp nearby ready to act and arrest SAMCRO, the Irish Kings and the Galindo Cartel members, all while giving them an encouraging speech to his men (at this chance he mentioned bringing "three criminal organizations to justice" which hints that he never had any real intention to let the Sons of Anarchy survive). His plans are foiled however by the appearance of none other than the Galindo Cartel members Romero Parada and Luis Torres, who reveal to Potter that they are undercover CIA agents and that the government is backing up the Galindo Cartel in hopes of bringing the others down for political motives. Then the two with a legal order, force Potter to surrender on his RICO plan and to give all the info from his case to them. Distraught he meets with Roosevelt and are both surprised and displeased with the results claiming that "the bad guys won today". He proceeded to give Roosevelt all the files on Juice, as he knows Roosevelt would want to free Juice personally of the racial blackmail. He confesses to Roosevelt that he does not like people too much and that he has great respect for him, the two parting ways with a handshake and in good terms.
He appears for a last time in the season in the voting for Charming Heights as Hale had found the investment of the Natsuki Family, Georgie's investors for his sex business. He then reveals to the court the true colors of the Natsuki Family, which Hale had hidden in purpose as a "Tokyo Fund" with all the information that showed they were the largest manufacturer of sex toys and pornography in the world, and also being involved in pedophilia. A very displeased Jacob Hale goes to him and asks Potter why he did that, and he replied that he "does not like" Hale, and then leaves while saying to himself that "the good guys needed a win" (following his failure on his RICO case). The vote for Charming Heights was then put on hold.