Lynn Michaels was an officer with the NYPD. When jogging through Central Park, Lynn was attacked by an armed serial mugger/rapist. Punisher and Michaels then teamed up to apprehend the criminal. From then on the two would call on each other a number of times.
Lynn Michaels was introduced to Marvel readers through Punisher: War Zone #7 "Mugger's Picnic" in 1992 and was created by writer Chuck Dixon and artist John Romita Jr.
Mayor Story Arcs
In The War Zone
Upon being attacked by the armed criminal, Punisher tackled him and fought him off but confused and shocked, Lynn pulled her sidearm on Punisher, allowing the criminal to get away. Explaining his intentions and that he'd been hunting the criminal, Lynn agreed to team up with Punisher and apprehend him together.
Identifying the armed criminal through the fingerprints he left on his own bullet shell casings, they tracked him down to his apartment, but after an exchange of gunfire, he escaped and ran for a passing train. Punisher jumped the train also but Lynn was left behind. Due to the scene at Central Park however, Lynn was identified as having worked with the Punisher by an onlooker and the assassin, Stiletto, followed Lynn back to her own apartment, hoping to find the Punisher through her.
Punisher, at the time having killed the mugger/rapist and two more assassins, went back to Lynn to see to his own wounds. While there, Stiletto, who had crept in and hidden in the dark, attacked and stabbed Lynn in the shoulder and Punisher shot him dead in retaliation. Lynn planted a kiss on him as thanks for saving her life.
Lynn Michaels crossed over to Punisher War Journal in issue #57 when Punisher called for her help in solving the "Vampire Killings" case, where she would this time save his life. She became a regular in the series and after becoming disgusted with the legal process when evidence against child killer Charles Dirkin was ruled inadmissable, she quit the force and went her own way. Shortly after, when Dirkin was imprisoned, Lynn sent him a package of cigarettes. When he went to his cell window to smoke, she killed him with a sniper rifle, having taken up the role of the Punisher.
Frank Castle Is Dead
The Punisher missing and presumed dead, the group VIGIL was out targeting vigilantes and went after Payback, Eddie Dyson. Lynn rescued him and together they formed a duo to better stand a chance against the group. Thery were however caught by VIGIL where Payback was serverely injured and Lynn was beaten. Escaping, they gained knowledge that Frank Castle was still alive and seen in Laastekist, Pennsylvania.
VIGIL following after them, they found themselves caught in a hard place and after recuperating from her own injuries in the wake of other battles, Lynn went to single-handledly take down VIGIL. This later led to the attention of mafia boss Rosalie Carbone, Mondo Pain, Blind Joe Death and then the Punishment Squad. The heat got too much, with an injured Eddie and her father also in the mix. They were on the run for so long when Lynn decided that Frank's life was definitely not for her. Chased by both the Punishment Squad's last men, Heathen and The Trust, Heathen killed the leaders of the Trust and allowed the three to escape, knowing that they were leaving the state for good. They escaped and retired to the Michaels Farm in Wisconsin.
War Journal II
Many years later, Lynn showed up working for SHIELD as a deep cover operative. Upon learning that Jigsaw had new plans to kill the Punisher, she went undercover with a new identity, Diamonelle.
Earning Jigsaw's trust, she got in on his operations in his mental institute where he was brainwashing the patients to become killers. In several twists, Lynn met with the Punisher under her new disguise and he didn't recognize her, she shot his then assistant Stuart Clarke and told him that Frank had killed his girlfriend Tatiana Arocha, she had Frank and Jigsaw arrested by SHIELD and then she had one of Jigsaw's patients shoot Jigsaw in his own cell before being arrested.
Lynn Michaels can also be found in Marvel Legacy, the 1990's handbook.