Donald "Donnie" Ryan

Kate Moretti's ex husband, who cheated on Kate with her best friend. He has recently transferred back to Chicago in an attempt to reignite his relationship with Kate. He is a lawyer and is usually very sceptical of Dr. Daniel Pierce's ideas and seeks to keep Daniel away from Kate.

Biography
Very little is known about Donnie's life, but it was mentioned in Season 2, Episode 8 Asylum that he was a former bartender and worked alongside Kate.

Because of this, he was able to cover and assist Kate when her father, who strongly dislikes Donnie because of Donnie's affair, went out of town for a couple of days, leaving Kate in charge of the bar for the weekend he was gone.

Personality
Donnie is something of a sceptic. He tends to doubt Daniel's ideas and dismisses them. He was also described as charming by Kate in S2, Ep8 when they reflected on their time working as bartenders together and she said the customers were so "dazzled" by his charm and good looks.

Kate Moretti
Donnie has a good relationship with Kate. Whilst she upon first seeing him after he got transferred back from DC was displeased to see him, he was less hostile and sought to try be civil with her. She rebuffed these attempts at first but eventually was willing to be kinder to him.

Over time they eventually reignited their relationship and soon began seeing each other again and during Season 3, Episode 1, Paris, he asked her to marry him, to which she replied "again" before accepting.

Dr. Daniel Pierce
Donnie and Daniel didn't initially get on at first, Donnie being dismissive of Daniel's theories and when Daniel said he wanted to take a prisoner to the university for a Brain Scan, he said it was a bureaucratic nightmare and was unwilling to go through with it.

Their relationship was not helped when Donnie openly asked Daniel on the witness stand during a court trial if he was a Paranoid Schizophrenic, a fact Daniel preferred to keep quiet. In later episodes he began questioning Kate as to why she felt the need to involve Daniel and he attempted to keep Daniel from Kate. Eventually however he became less hostile toward Daniel and even became willing to work with Daniel such as during Season 2, Episode 6, Defective, when the pair worked to prove a medical implant was defective and was the cause of several deaths. Or during Season 3, Episode 2, when he asked Daniel to educate a jury on what Stockholm Syndrome was and how it affected people, to help him in prosecuting a human trafficker.