1. He was born in the North of England, but attended school in London all his life. He went to medical school in England and did his specializing in Chicago, where he's lived since. As a consequence, his accent is a bit all over the place. He mostly has the posh London accent, but the Northern creeps in now and then.
2. His wife, Samara, is also British. They were seated next to each other on a flight from London to Chicago, both of them having been home to visit family. By the end of the flight, Forrester had her phone number and she had decided she was going to marry him.
3. He has a younger brother, Brandon, who is a GP. Both he and his brother are named for Jane Austen characters. Mr. Darcy from Pride & Prejudice and Colonel Brandon from Sense & Sensibility. His mother taught English (she's retired) and his father is a judge who insists he will never retire and, indeed, will probably be found dead at his bench one day.
4. Has a Celtic knot tattoo between his shoulder blades that he got as part of bet undertaken when he was extremely drunk, during his med school days. He's nonetheless rather fond of it.
5. He wanted to be a surgeon but didn't have steady enough hands for it, so he switched out of the programme. His specialty is Infectious Diseases (especially tropical ones), but he acts as sort of a 'House-like' figure for Cook County. If someone is sick and they don't know why, they call Forrester.
6. Plays the piano a little, but once again didn't have the hands to be great. He has one song he can play - Moonlight Sonata. He spent a very long time learning it and, after having done so, felt he didn't need to learn any more. It's very impressive at parties.
7. Is terrible with most languages. He has no ability to recreate the proper sounds and no matter what language he's trying to speak, it just sounds like English. He understands a lot of Hindi, but has learnt to just keep to English with his in-laws to avoid the teasing.
8. Spent his gap year with the Red Cross in Africa, which encouraged his interest in Infectious Diseases.
9. Has a dog, Odysseus, who Samara adopted on a whim from the Humane Society. Forrester came home in the middle of the night after a long shift to find the mutt puppy had suddenly appeared and was sleeping on his pillow. Ody is fond of stealing Forrester's stethoscopes.
10. After what happened during the Sleeping Sickness Epidemic and a few more encounters with Harry Dresden (mostly in the ER), he's pretty much convinced about the whole 'magic is real' thing. Thankfully, he's not encountered anything too weird since and has managed to remain with both feet planted in the 'real' world. Well, maybe with a pinkie toe in Dresden's world.