Stiliyan Petrov, once described by an American newspaper as a "multidimensional character", is that rare animal: the Eastern European sportsman who has written a bestselling book.

OK, You Can Call Me Stan was a bestseller only in Scotland but this was still an achievement for a Bulgarian of whom little is known outside Glasgow and Sofia.

Now, however, his fame will extend to Birmingham where Petrov will earn his living for at least the next four years.

When he joined Aston Villa yesterday, in an #8 million move from Celtic, he was absorbing the sunshine in Sofia and not in the least bit surprised that he was being reunited with Martin O'Neill. Petrov has wanted this for weeks.

It was clear, from the moment that O'Neill took over as manager of Villa on August 4, that Petrov was a target. The two men go back six years, to the summer of 2000 when Petrov felt dispirited and when O'Neill put into motion a plan to revive Celtic.

Five years later, when Petrov's tome hit the bookshelves, readers found that O'Neill had been given a prominent role as the author of the foreword. O'Neill wrote the foreword himself, without the need of a ghostwriter, just as he writes his own column in the Aston Villa News & Record.

There is a passage in the book that says much about Petrov and O'Neill and also, perhaps, about their relationship.

"There is a popular saying in football that no individual is bigger than the club but Martin O'Neill was probably as near as you will get to that logic being dismissed," Petrov wrote.

"He is a top-class manager. He put Celtic back on the map. I'm so glad that he was appointed, as I really do not know where I would be now without him... I truly believe that it was Martin O'Neill who saved my career."

To some, these words could be the hyperbolic meanderings of a man with little interest other than to sell books, but it is more likely that these words are those of a grateful player who is in awe of a distinguished manager.

Nevertheless, on this, the final day before the transfer window closes, there are Celtic supporters contacting radio stations with criticisms of Petrov.

The player is seen as lacking loyalty - he submitted a transfer request last April, before O'Neill took over at Villa Park - and chasing the limitless money of the Premiership.

But Petrov, who boasts a Scottish accent, had gone as far as he could with Celtic. He had played in a European final (the Uefa Cup in 2003), won the Scottish League title and the Scottish FA Cup. Villa presents a new challenge, as does the Premiership.

Petrov, aged 27, does not conform to the standard Bulgarian stereotypes. He is not surly, looks and thinks like a Western European and plays like a German. He is a creative midfield player who can tackle like a defender. Aged only 21, he was handed the captaincy of Bulgaria after a vote by team-mates. He was sent off when Bulgaria played Denmark in Euro 2004.

The relationship between Petrov and O'Neill is similar to that of John McGovern and Brian Clough in the Seventies. O'Neill is Petrov's mentor.

"Overall, O'Neill was a clever and talented man," Petrov said. "Every Friday [in training] we played a game between the younger players and the old guys in the squad and the worst player had to wear the dreaded yellow jersey.

"His team-talks were exceptional and the way he motivated players was unbelievable. He didn't talk for hours on end, he just kept it short and sharp. That's the way he was before a game and even more so at half-time, when there's only a few minutes to say the important stuff.

"Martin O'Neill would criticise you if he felt you hadn't played well but he would do it behind closed doors and not in public. He didn't criticise for the sake of it [2014] there was also merit in his judgment [2014] he just hated losing football games. O'Neill was always honest."

Honest, yes; but cagey, also. For virtually the whole of August, O'Neill seemed to be the only man who refused to talk about the possibility of Petrov moving to Villa. Petrov's relocation to Villa Park was the worst-kept secret in football.

Nevertheless, confirmation arrived... from the manager of Portsmouth. "I think you will find Petrov has gone to Aston Villa," Harry Redknapp said on BBC 5Live. "That is the plan and we wish him all the best."

Two days later, Petrov and O'Neill were reunited professionally and were looking to do to Villa in 2006 what they did to Celtic in 2000.

Petrov was under-achieving during his first season with Celtic. Kenny Dalglish and John Barnes were the joint managers and morale was low. Towards the end of the season, with Barnes now departed, Dalglish inspired Petrov but this was nothing compared to the effect that O'Neill would have.

"Martin was straight to the point and asked me what position I preferred to play in," Petrov said. "When I told him it was the centre of midfield, he promised me a chance to play there.

"By giving me that opportunity, there could be no excuses if things didn't work out for me during his stew-ardship. He also told me to improve my fitness if I wanted to play in his team."

Petrov no longer needs to improve his fitness. He will lead Bulgaria out against Romania in Bucharest on Saturday, then against Slovenia next Wednesday, before he makes his Aston Villa debut at West Ham United on September 10.

O'Neill clearly intends to fashion Villa in his own image.

The arrival of Petrov is the first stage of the transformation.