A “self-help” guru was charged this week with sex-trafficking his female members, keeping them as “slaves,” and branding them with his initials.

Federal authorities arrested Keith Raniere, the founder of NXIVM, a secret multi-level marketing cult, on Monday for allegedly forcing members to engage in sex acts.

Raniere, 57, who is known as “The Vanguard,” previously fled to Mexico last year ahead of a federal probe and New York Times investigation exposing the cult leader's alleged sex-trafficking ring. He was arrested below the border and is now in custody in Fort Worth, Texas.

According to court records, Raniere had sexual relationships with a rotating group of nearly 20 women, in which they were allowed to only have sex with him. NXIVM's curriculum, according to court documents, revealed men were allowed to see multiple women, but women were to remain strictly monogamous.

More than 20 years ago, Raniere, an alumnus of Rensselaer Polytechnic Institute founded Executive Success Programs (ESP), a series of workshops to "actualize human potential." In 2003, Raniere launched NXIVM, a group claiming to offer members a "new ethical understanding" allowing "humanity to rise to its nobility possibility."

That year, a parent, who formerly backed Raniere's program, told Forbes that he worried about his daughters whom he hadn’t spoken with in months. “I think it’s a cult,” that parent, Edgar Bronfman, declared. In 2009, Raniere filed a defamation claim against the parents, citing that article.

Ex-NXIVM members know all too well the cult leader's allegedly manipulative tactics. Raniere's classes can cost up to $5,000 for a five-day workshop, according to court documents, and because members often find themselves in debt for the courses they take, they are obliged to work for the company to pay it off. During the cult leader’s birthday in August, members are expected to pay $2,000 or more to gather in Silver Bay, New York to honor him for “Vanguard Week,” court records reveal.

Raniere also allegedly created DOS, a secretive sex cult operating in New York, Canada, and Mexico. The acronym stands for "Dominus Obsequious Sororium" which, according to one DOS member, translates to “master over slave women,” according to court documents. DOS operates as a pyramid with levels of slaves headed by masters. The “slaves” are expected to recruit slaves of their own, thus becoming masters themselves.

In a statement to ABC News, FBI’s New York Field Office Assistant Director William F. Sweeney Jr. blasted the cult leader.

“As alleged, Keith Raniere displayed a disgusting abuse of power in his efforts to denigrate and manipulate women he considered his sex slaves,” Sweeney, Jr. “He allegedly participated in horrifying acts of branding and burning them, with the cooperation of other women operating within this unorthodox pyramid scheme. These serious crimes against humanity are not only shocking, but disconcerting, to say the least, and we are putting an end to this torture today.”

Last year, ABC News 20/20 interviewed ex-DOS member Sarah Edmondson, who joined the group believing it was a sorority to empower women. In a photo obtained by the newsmagazine, Edmondson was branded by a cauterizing pen with what appears to be Raniere’s initials.

Edmonson told ABC the “pain felt worst than childbirth.” Another ex-DOS member told investigators that Raniere burned women with his “initials” in tribute, according to court documents.

In a pitch to become a “prospective slave,” the women were told they had to provide “collateral,” which, according to court documents, included sexually explicit photos and confessions of “damning” stories about themselves. The goal of DOS was to “eradicate weaknesses,” the curriculum claimed, because women had “overemotional natures.”

One woman, who worked directly under Raniere, said she could be “paddled” or “put in a cage” if she failed to comply with his assignments. “Masters” regularly groomed “slaves” for sex with Raniere and also forced women to have sex with him. While on assignment, masters allegedly committed the “slaves” to low-calorie diets because Raniere preferred “exceptionally thin” women.

The “slaves” also had to perform “acts of care” including bringing masters coffee, carrying their luggage, cleaning their homes, and retrieving lost items for them, court documents claimed. The slaves allegedly worked under NXIVM and were delegated tasks such as transcribing and reviewing dense stories written by Raniere.

In a statement on Raniere’s website, he said the “sorority” is not linked to NXIVM. Also, he claimed experts he hired to evaluate the group say members of the sorority are “thriving, healthy, happy, better off, and haven’t been coerced.”

“I feel it is important to clarify the sorority is not part of NXIVM and that I am not associated with the group,” Raniere said in a statement. “I firmly support one’s right to freedom of expression, so what the sorority or any other social group chooses to do is not our business so long as there is no abuse.”

He added: “The picture being painted in the media is not how I know our community and friends to be, nor how I experience it myself. However, as an organization and as individuals, we felt it was imperative that we hire experts to ensure there is no merit to the allegations.”

Emails linked to Raniere’s account reveal otherwise.

According to court documents, a search of Yahoo confirmed correspondence associated with the group were personally sent by Keith Raniere and “supports the conclusion that Raniere created DOS.”

U.S. Attorney Richard Donoghue ordered Raniere to be detained pending trial. If convicted, he could face 15 years to life in prison.