I find it difficult to choose my favourite - there are two candidates.
David Dankworth, my music teacher, helped me realise I love performing. But my English teacher, Mark Wilson, was a particularly special man. My high school was in the town of Joliet, Illinois, about 50 miles south of Chicago. I was quite badly behaved, but I never got caught. I would often sneak off-campus for lunch with my mate, whose mother was the dean. I would also skip class and go down to the music room and hang out there if I didn't want to go to maths.
Mark Wilson was only my English teacher for one year before he noticed my potential and moved me up to the Gifted Programme, which meant changing teacher. But he stayed with me for speech coaching - the school had a speech team competing against other schools, reciting scenes and monologues from plays. Mark coached me in that all the way to the state championships.
He would discuss things with you, so he felt like a friend.
He made you feel special - a lot like Robin Williams in Dead Poets Society.
He never let you think anything you said about literature was wrong - all contributions were valid. In his early to mid-30s, he was the youngest teacher in the school. Medium height, heavy-set, with a beard and curly hair, he wasn't particularly trendy - he always wore corduroy pants or jeans with shirts and a sweater. But he had a very cool attitude. We could talk to him about drinking and partying and he would not be at all judgmental of us. He wouldn't necessarily agree with us, but he would give a neutral opinion. And you could swear around him, which we thought was excellent.
He must have loved his job. He lived on the north side of Chicago and commuted 50 miles every day to the school. Sometimes at the weekend he would invite some of us up to the city if there was a festival going on.
Joliet was a quintessentially middle-class conservative town, so to go into the city was a huge deal.
I never kept in touch with either teacher. I hope they realised what a great effect they had on the lives of the young people they taught
John Barrowman appears in the BBC's science fiction dramas, Torchwood and Doctor Who. He is also a judge on Any Dream Will Do, the BBC1 search for a male lead in the revival of Joseph and the Amazing Technicolour Dreamcoat.
Torchwood: Another Life, read by John Barrowman, is available on CD (Pounds 15.99, BBC Audiobooks). He was talking to Mark Anstead