Ever since they first clashed when they met at the negotiating table, George Parker and Michelle Rhee have had a somewhat unorthodox relationship.
"She used to call me and say `I'm getting ready to throw you under the bus'," Mr Parker said, laughing.
In 2007, he was president of the Washington Teachers' Union (WTU) in the US; Ms Rhee had just been appointed chancellor of Washington DC's public schools.
She wasted little time in making her presence felt. In her first year in the job, the highly controversial official closed 23 schools and dismissed 36 principals. Ms Rhee quickly gained notoriety as the education reformer the unions loved to hate.
"I began to get some grey hair," Mr Parker told TES. "She came in with a bang, with all these reforms. I remember plotting how we would get rid of Michelle.
"I was like, `We'll listen to what you say, but we'll get you, too. Like we got the rest of them, right? We'll get you, too.'"
Little could Mr Parker have imagined that, four years later, he would be on the same side as his erstwhile opponent.
In 2010, after two and a half years of tense negotiations, the WTU and the school district signed a groundbreaking agreement. The city's teachers would receive a 21 per cent pay rise over five years, but would also see their pay tied to performance. And they would lose out on "seniority", a controversial system that afforded job protection to longer-serving teachers irrespective of performance.
Within a matter of months, both Ms Rhee and Mr Parker were out of a job. Ms Rhee resigned when her boss, the city's mayor, Adrian Fenty, was voted out, partly in response to her controversial reign over the city's schools.
Mr Parker lost the union presidency election to a rival who accused him of ceding too much ground to Ms Rhee.
Then, in 2011, there was an announcement that shocked the US educational establishment to its core: Mr Parker had been appointed senior fellow of StudentsFirst, the non-profit organisation founded by Ms Rhee to promote educational reform.
But for Mr Parker - who last week was given a rapturous reception at the Conservative Party conference in England - this remarkable journey was triggered by pragmatism.
Before Mr Fenty was elected mayor in 2007, Mr Parker explained, the city's politicians were at the mercy of the unions, which bankrolled their election campaigns.
"If the (schools) superintendent wanted to negotiate something that was a no-no, all I had to do was call the politicians and say, `Look, your boy's talking crazy. You need to give him a call.' It worked beautifully, right?"
Until, that is, Mr Fenty transferred the management of the city's education system to Ms Rhee. As a result, Mr Parker's political influence disappeared overnight.
"I had nowhere to go," he admitted. "Before, I just refused to discuss (some issues). Now I was going to have to defend positions. It made me begin to analyse who I was."
Mr Parker's internal ideological struggle came to a head during a school visit when a student asked what his job entailed.
"I told her, `I make sure you have the best teachers'," he said. "When I was getting ready to walk out, this little girl came up to me and hugged me. And so of course I wanted to know why. She said, `Because you said you care about us and you make sure we get the best teachers.'
"So I'm driving back to the office and I say to myself, you lied to that little girl. You don't really make sure she has the best teachers. You just spent $10,000 in arbitration to put a bad teacher back in front of children.
"Under no circumstances would you let that teacher even get near your grandchild, but you'd put that teacher in front of students like that little girl."
After this wake-up call, Mr Parker began to take unprecedented stances for a union leader, not least in agreeing to abolish seniority and introduce performance-related pay.
"I can't tell you the number of other union presidents that called me and said `Don't do it'. But I said, `Look, this just makes sense to me now.'"
The argument for reform has already been won, according to Mr Parker. "The train was leaving the station, and I was still standing in front pushing. The train was too powerful. Reform is coming. People are not going to sit back and see an education system fail their children for ever."
Teachers, too, had a role to play in weeding out their underperforming colleagues, Mr Parker argued. "I used to say to teachers, `It's none of your business what he does next door. That's not your job.' Now I say to teachers, `It is your business.' Teachers have to raise the standard of the profession.
"If you saw this guy, as a teacher, sexually abusing a child, you'd report it. Well, guess what, that teacher next door is not teaching - that's educational abuse. As a teacher, you've got a responsibility to advocate for children."
Heart and soul
George Parker was born in 1950 in rural North Carolina. In his youth, he played an active role in the African-American civil rights movement, before carving out a career in the entertainment industry, as a singer and keyboard player in soul bands Act One and Special Delivery.
When the gigs started to dry up, he sought work as a supply teacher and soon realised that the classroom was the place for him. He taught maths for 30 years in Washington DC schools.
Mr Parker was president of the Washington Teachers' Union from 2005 to 2010. The following year, he was appointed senior fellow at StudentsFirst, a campaigning and lobbying organisation that describes itself as "a grass- roots movement to reform America's public education and keep our best teachers in the classroom".