Russell Brand is facing accusations of rape, sexual assaults and emotional abuse over a seven-year period.
The actor and comedian is also said to have behaved inappropriately at work during the height of his fame, including by undressing, making sexual remarks and acting aggressively.
Brand denies the allegations, revealed in a joint investigation by the Sunday Times, the Times and Channel 4's Dispatches, and says his relationships have been "always consensual".
Here, BBC News sets out what the star is accused of - and how he has responded. Warning: this article contains some graphic details about the alleged acts.
Rape, sexual assault and emotional abuse
Four women are alleging sexual assaults between 2006 and 2013:
One woman alleges that Brand raped her without a condom against a wall in his Los Angeles home. She says Brand tried to stop her leaving until she told him she was going to the bathroom. She was treated at a rape crisis centre on the same day, which the Times says it has confirmed via medical records
A second woman, in the UK, alleges that Brand assaulted her when he was in his early 30s and she was 16 and still at school. She alleges he referred to her as "the child" during an emotionally abusive and controlling relationship. Looking back, she says, he "engaged in the behaviours of a groomer"
A third woman claims that Brand sexually assaulted her while she worked with him in Los Angeles. She alleges she repeatedly told Brand to get off her, and when he eventually relented he "flipped" and was "super angry". She says he threatened to take legal action if she told anyone else about her allegation
The fourth woman has alleged being sexually assaulted by Brand in the UK and him being physically and emotionally abusive towards her
How has Brand responded?
On Friday, the day before the investigation was published online, Brand shared a video on social media where he denied the allegations.
In it, he denied "serious criminal allegations" he said were to be made against him, and said his relationships "were absolutely, always consensual".
Russell Brand allegations
The actor and comedian said he had received letters from a TV company and newspaper containing "a litany" of "aggressive attacks".
The 48-year-old said he believed he was the subject of a "co-ordinated attack" and was going to look into the matter because it was "very, very serious".
Within hours of the allegations being published on Saturday, Brand performed a scheduled comedy gig at the 2,000-capacity Troubadour Wembley Park Theatre in north-west London, as part of his Bipolarisation tour.
During the set, Brand alluded to the accusations but did not address them directly. He told the audience there were things he wanted to talk about but could not.
On Monday, the remaining dates for his tour were postponed.
What are the other allegations?
Other claims made as part of the investigation relate to Brand's allegedly controlling, abusive and predatory behaviour, and inappropriate behaviour in the workplace.
During the years covered by the allegations, Brand had various high-profile jobs at different times, including at BBC Radio 2 and Channel 4, and as an actor in Hollywood films.
His attitude towards women was "an open secret" in radio and TV production, sources told the Sunday Times.
It is alleged that Brand would undress in the studio while working as a presenter on BBC Radio 6 Music. Dispatches also said Brand made sexual remarks on air about a newsreader, which he later implied he had been told by BBC production staff to apologise for.
The Sunday Times said sources had told the newspaper that a complaint was made to BBC management about an "alarming display of aggression and disrespect" from Brand. This is said to have included Brand throwing objects across a Radio 2 studio and urinating in a bottle in front of staff and guests, including a minor.
The newspaper also said TV researchers and runners working on Channel 4 shows alleged that Brand would get staff to approach young female audience members so he could meet them after filming, some of whom were later upset by how they felt they had been treated by him.
Other allegations include:
As part of a phone conversation broadcast on his radio programme, Brand offered to bring a female employee with him to meet Jimmy Savile - and agreed, at Savile's request, that she be naked
Brand's personal assistant claims she saw him showing friends intimate photographs of women
Two former crew members on Big Brother's EFourum show claim they felt like they were working as a "pimp" for Brand
A runner says Brand flashed his penis and insinuated she could give him oral sex when she walked into his dressing room
A female comedian claims Brand chased her backstage and bit her face when they gigged together, continuing after she made it clear she felt uncomfortable
Separately, since the story broke, a woman has come forward alleging Brand exposed himself to her and then laughed about it minutes later on his BBC radio show in 2008. That incident, which allegedly happened at the BBC's Los Angeles office building, was the first time that Brand has been accused of sexual misconduct and then heard discussing it.
What have TV, radio and production companies said?
On Sunday, the BBC noted Brand worked on BBC radio programmes between 2006 and 2008, and said it is "urgently looking into the issues raised" by the allegations. It has announced a review of Brand's time at the BBC.
In an earlier statement on Saturday, the BBC said it had "clear expectations around conduct at work", adding: "We will always listen to people if they come forward with any concerns, on any issue related to any individual working at the BBC, past or present."
Following the allegation Brand exposed himself in Los Angeles, the BBC said it was sorry to hear the claims and would investigate them as part of its review.
Channel 4 has announced its own internal investigation and encouraged "anyone who is aware of such behaviour to contact us directly".
In a statement on Sunday, it said it was "appalled" to learn of the "deeply troubling allegations, including behaviour alleged to have taken place on programmes made for Channel 4 between 2004 and 2007".
It said it was determined to understand what went on and said it had found no evidence that the alleged incidents had been previously brought to its attention.
Separately, production company Banijay UK has also launched an "urgent" internal investigation into allegations about Brand's time presenting programmes screened on Channel 4 and E4.
Have the police responded?
In the wake of the allegations made against Brand, the Metropolitan Police said on Monday it had received a report of an alleged sexual assault in Soho, central London, in 2003. The Met said officers were in contact with the woman and providing support to her, adding: "We continue to encourage anyone who believes they may have been a victim of a sexual offence, no matter how long ago it was, to contact us."
The force first spoke to the Sunday Times on Saturday. It has since made further approaches to the paper and Channel 4 "to ensure that any victims of crime who they have spoken with are aware of how they may report any criminal allegations to police".
On Sunday, the Los Angeles Police Department said it had not been notified "of any incidents, reports or allegations regarding Russell Brand or any of the accusers".
It could not immediately confirm reports of an LAPD officer being alerted by a rape crisis centre in 2012 about one of the accusers being treated there following an alleged incident with Brand.