Harry describes him as short, over-weight, balding,beady eyes, weak chin. His clothes were rumpled with food stains. All of htis served to conceal a razor sharp intellect. He was a sharp cop and ruthless at tracking killers. 
In Fool Moon, He was an overweight, balding man who doubted Dresden's abilities and credentials because he doesn't believe in magic. But, he believes Harry when when he says he's not connected to Marcone. 
In Storm Front, Ron's at the Jennifer Stanton's murder scene and constantly bugs Murphy not ot believe Harry. Later, Murphy uses him as a witness when talking to Harry; he wants to arrest Harry.
In Fool Moon, Carmichael pulls Harry away from the Loup-garou. Soon after he is killed when the Loup-garou tore through the station. He lost his life protecting Murphy. His funeral was attended by Murphy and Dresden.
In Ghost Story, He makes a return as his 30 year old self working at Between, a.k.a Purgatory.