Russell was a Police CID officer who had a brief relationship with Ian Gallagher in Series 3. Russell and Ian had sex on at least one occasion, the next day Russell told Ian that he worked in security but this was soon revealed to be a lie.
After a Police chopper took infra red pictures of the Gallagher attic and discovered the Cannabis plants Carl had been growing for the Maguires, the Police Drug Squad raided the house. Ian was surprised to find Russell among the police but Russell was worried.
Ian asked Russell to do what he could for Carl and Russell agreed to take a statement and release Carl without caution or charge, though this later made it appear that Carl had given evidence against the Maguires. The real "grass" has been Shane Maguire, who gave evidence against his own sister because she was given a higher position in the Family Business. Before anyone knew this however, Ian appealed to Russell to give him the informant's name to get the Maguires off Carl's back but Russell told him that he had only released Carl so Ian wouldn't reveal that they had sex and didn't want to see him again. After going back into the Police Station another officer asked who Ian was and Russell replied "just another Chatsworth arse hole."
It is possible that Russell was married or at least had children, as when Ian goes to the Police Station to ask him about the informant he stands outside and signals to Russell, but before he exits an officer is heard asking how the kids are, to which he replies "fine". If he was married it would explain why he risked his job by releasing Carl without charge or caution just to make sure Ian didn't tell anyone that they had sex.