Sorrell is suing Marco Benatti, Marco Tinelli and the Italian media company FullSix Spa, for libel and breach of privacy.
He has accused them of disseminating blogs containing a "host of libels" and a "vicious" jpeg image of himself and female executive Daniela Weber, chief operating officer of WPP Italy, and of labelling them "the mad dwarf and the nympho schizo".
Ms Weber is also suing for breach of privacy.
Sorrell's counsel, Desmond Browne QC, told Mr Justice Eady in London that the blogs alleged repeated criminal activity and a career built on money laundering, and attacked every aspect of 62-year-old Sorrell's character.
Browne said: "We say these go to the very heart of the plaintiff's integrity and professional reputation and therefore merit an award at the top end of the scale for libel awards". He added: "Although he and we know the allegations were completely untrue, they remain damaging in an industry as small as advertising."
Sorrell also had to tell his three sons of the libels before they heard them from others, the court was told.
Giving evidence, Sorrell said: "It is difficult in open court, and maybe there will be an opportunity in private to discuss my reaction to the jpeg in particular, but I can't conceive of any way that anybody could have sought to undermine my professional and personal reputation in a more vengeful and vindictive way.
"I can't conceive of it getting much worse than this," Sorrell said.
He said that, since January 2006, he had asked the defendants to show, "transparency, trust and openness" and that his only objective was to "get to the truth'".
Sorrell branded a defence concession last month that someone in FullSix -- not Benatti or Tinelli -- might have been involved in the dissemination of the jpeg email and the libellous blogs last March as "weasel words" in an attempt to get off the hook.
Browne has told the judge, who is hearing the fiercely contested case without a jury, that there was "overwhelming forensic evidence" against Benatti, FullSix's founder and his "lieutenant'", chief executive Tinelli.
Sorrell said that his experience of Benatti was that he only acted if he was "cornered". "As we have seen in this action, he seems to lash out emotionally and even violently in many situations when he feels himself up against it.'"
Browne said that the case flowed from the aftermath of a broken close friendship between Benatti and Weber, whom she had known for over 20 years, and the consequences of Sorrell's termination of Benatti's consultancy as the country manager for WPP in Italy.
In March 2006, it is claimed, Benatti's Italian lawyer rang WPP's lawyer and told him that Benatti would be devoting the next few years to destroying Sorrell and WPP and it had now become a personal battle.
Browne said Benatti and Tinelli had the motive and the opportunity to have constructed the campaign.
"We say that they also had the requisite knowledge -- both knew of the contents of the blog, which would be necessary for its authorship and in the case of Tinelli, knowledge of the requisite IT skills to cover up those who were responsible for it.
"Nothing has come to light to suggest that there are any other possible suspects and, gradually, analysis of the forensic evidence has filled in the jigsaw.
"As often happens with jigsaws, at the end of the day it is not complete in every respect, but, in this case, it leaves no doubt whatsoever of the guilt of both Benatti and Tinelli", Browne said.
In his witness statement, before the court, Sorrell said that he believed that Benatti considered that attack was the best form of defence.
He said he felt that it was no coincidence that in December 2005, the month before the consultancy was terminated, Benatti gave him Christmas presents of three books -- 'The Art of War' by Sun Tzu, 'The Prince' by Niccolo Machiavelli and Carl von Clausewitz's 'On War'.
"Sun Tzu was a famous Japanese general whose book notoriously sets out his views on resourcefulness, cunning, the profit motive, secrecy, speed, surprise, deception and manipulation.
"He famously said that 'Invincibility is in oneself, vulnerability is in the opponent'. This was clearly meant to be a message to me from Mr Benatti.
"These were unlike any present he had previously sent me, he usually gave me a WPP Italy diary each year."
Sorrell said that when he saw the anonymous blog called 'Don Martino', on March 21, last year, he was "horrified".
"It accused me of criminal fraud, deception and money laundering. It accused me of allowing 'subordinates' to go to prison to cover up for my criminal activities. It even suggested that I had built my entire career through money laundering," Sorrell said.
"I found these allegations, as well as the implication that I would stoop to the most heinous of criminal activities in order to get what I want, utterly outrageous and disturbing.
"I felt that the use of the word 'Don Martino' and 'wise guy' was intended to reinforce this impression, suggesting that I had some sort of 'mafia' connections.
"They impugned my integrity and honesty, both professionally and personally, making me sound like a ruthless criminal.
"I cannot think of a more comprehensive attack on my character."
He said that he found the task of telling his three sons "terribly upsetting".
The brothers, aged 32, 31 and 29, all work at merchant bank Goldman Sachs in London.
Sorrell said: "Having read the weblog I instantly thought of Mr Benatti. As I have explained, he was the person with the most obvious motive to do this. In addition, so many of the aspects of the blog pointed to Mr Benatti."
He said that within hours of closing down the blog on March 23, "grossly offensive images were sent out by a series of emails".
"Not only do I believe that it is no coincidence that these offensive emails started to be circulated immediately after my lawyers had succeeded in closing down the weblog, there is forensic evidence to prove the link between these two actions."
He said that he would deal with those matters in a separate confidential statement.
Sorrell said that he was shocked at the end of May 2006 to find that an almost identical weblog had been posted on various other internet sites.
He said the new blog contained the following "tell-tale message": "Don't mess with Don Martino. Don Martino is good. He's real powerful.... Really sorry to have disturbed you Don Martino, but if you have a problem with what we write, please stop bullying blog sites and post your comments..."
Sorrell said that he was appalled when he saw the initial list of recipients of the weblog email, since it included numerous influential people in the advertising and communications industry within the UK.
"It also makes clear that the defendants' attack on me had been carefully orchestrated."
The defendants deny libel and breach of privacy.