Hi Polyhmnia
Will do my best but am sure others have better memories..
Capitaine Laure Berthaud - totally driven cop, very loyal to her crew. Sometimes bends the rules to get what she instinctively knows is the right result. In series 2 fell in love with an undercover agent - ended badly. Current relationship good - started in series 3.
Gilles or Gilou - great copper but a bit too fond of prostitutes & drugs - often makes mistakes which Laure has to cover up, eg shooting a drug dealer in the crotch when he wasn't supposed to have been in the house. Has lots of sources etc in the 'underworld'.
Judge Roban - very fair and honest prosecutor who is almost obsessive at getting to the truth of his cases ( French justice system is inquisitorial, not adversarial, so judge has very far-reaching investigative powers). His cases usually run as a sideline to the main cop investigation. In series 3 he found corruption in a Paris suburb which led to the mayor - was warned to back off by mayor's high-ranking powerful friends but didn't. End result was he got taken off his job after his stagiare committed suicide (was caught between the two sides). A good friend of Laure and Pierre.
Pierre - used to be a prosecuting lawyer, now turned criminal defender ie now independent instead of acting for the State. Is now working in partnership with Josephine Karlsson. Upstanding & moral, but she's gradually getting to him..
Josephine Karlsson - criminal defender, pretty amoral and ends up with very nasty clients/mentors. Her mentor was Szabo - mega unscrupulous, friend-of-crooks defender. She's escaped his clutches and set up as an independent lawyer. In series 3 tried to go a bit straighter but always ends up dragged back in to the shady side.
HTH, sorry for any errors everyone else...