Jonathan Widmark was the head of the Operation Winter's End task force that aimed to take down Eddie Winter. His work was complicated from the outset by the fact that Winter managed to buy off or plant moles in almost all of Boston metropolitan area police department, with the sole exception of Cambridge, where the task force's command center was set up. To minimize the risk of infiltration, Widmark tapped Commissioner Widmark in Chicago, who transferred his ace detective, Nick Valentine, under his command. Widmark was excited to have Valentine heading the task force, believing him to be a critical asset in tracking down Winter's holotapes and taking the mob boss down.
It wasn't to be. The task force was a sham, meant to distract the criminal families of Boston. The BADTFL was working together with Boston's District Attorney to that end, and Winter was the means to achieve this ambitious goal. In return for his cooperation, Winter was granted immunity from prosecution and simply walked. The Winter's End task force was disbanded as soon as its purpose ran its course, leaving the policemen out in the cold. Nick Valentine was particularly affected by the loss of his fiancee, gunned down by Winter's thugs.
The move shocked and angered the people of Massachusetts, while Captain Widmark was forced to publicly clear Winter's name and thank the BADTFL, in a humiliating statement before the cameras. It also surprised the press, which was quick to point out the allegations turned up by the investigation. Captain Widmark decided to help ease Valentine's loss by ordering him to take part in an experimental CIT brain scanning program... And granting him immortality when the brain scan was used in an Institute experiment over a century alter to create a special kind of synth.
Jonathan Widmark is mentioned only in Fallout 4.