Below is an excerpt of the EN10 Mark Kennedy ('Mark Stone') profile at the former Undercover Research Group wiki, which also includes an early timeline of his activities during his time in his undercover.
Both were written soon after his exposure in 2010 and last updated in 2012, so before the Undercover Policing Inquiry started and Kate Wilson's case in the Investigatory Powers Tribunal was concluded.
EN12 Mark Kennedy ('Mark Stone') was an NPOIU undercover officer who operated from 2001 to 2009. Although based in Nottingham for most of his deployment, he infiltrated groups across the UK and Europe. He was exposed as a police officer in October 2010 by activists who no longer trusted him. His undisclosed involvement in an action against Ratcliffe Power Station led to a trial against dozens of activists collapsing.
Kennedy had quite a few sexual relationships, some long-term. His exposure led to several other undercover officers being exposed and marked the start of the spycops scandal.
After he left the police under a cloud, he returned to his activist friends to collect information to sell to corporate intelligence firms, Global Open amongst others.