Leon Wildes, a prominent immigration lawyer best known for his landmark, yearslong fight in the 1970s to prevent John Lennon from being deported and enable the former Beatle to receive permanent residency in the U.S., has died at age 90.

Wildes died Monday at Lenox Hill Hospital in Manhattan. His son -- immigration attorney and Englewood, New Jersey Mayor Michael Wildes — said that he had been in failing health after a series of strokes.

“Dad felt he effectively lived the American Dream for a kid from Olyphant PA and spent his life facilitating the same experience for scores more,” said Michael Wildes, who is also the managing partner for the firm his father helped start, Wildes & Weinberg. “He was beloved by his family, was extraordinarily humble, and beloved by our Bar.”

Leon Wildes was a graduate of the New York University School of Law who co-founded Wildes & Weinberg in 1960 and, by the end of the decade, had gained enough stature to serve as president of the American Immigration Lawyers Association. His name would become part of musical and political history after an old law school classmate, Alan Kahn, called in 1972 and told him that Lennon and Yoko Ono needed his help getting their visas extended.

Wildes agreed to meet with the couple at the Manhattan offices of Apple Records, the label founded by the Beatles in the late 1960s. But he did have one embarrassing confession about Lennon and his artist wife.

“I have no idea who these people are,” he told Kahn, later saying he misheard their names as “Jack Lemmon and Yoko Moto.”

What Wildes initially thought would be a formality turned into one of the most dramatic legal struggles of the era. Lennon and Ono had moved from England to New York City, trying to track down Ono’s daughter from a previous marriage, Kyoko Chan Cox, whom her ex-husband had abducted.

John and Yoko also were active in the New Left politics of the time, opposing the Vietnam War and backing efforts to defeat President Richard Nixon in his bid for re-election. With the minimum voting age lowered from 21 to 18, Lennon’s plans included a 1972 tour of the U.S. that would potentially attract millions of young people.

As government files later revealed, some Nixon supporters feared that Lennon could damage Nixon politically. In a February 1972 memo sent to Sen. Strom Thurmond, a South Carolina Republican and a member of a Senate subcommittee on internal security, aides recommended a “strategic countermeasure,” terminating Lennon’s visa. (The government would also try to deport Ono, a Tokyo native, but she was granted permanent residency in 1973).

Thurmond forwarded the memo to Nixon’s attorney general, John Mitchell, whose deputy, Richard Kleindienst, contacted the Immigration and Naturalization Service. In March, the INS informed the British rock star that his visa would not be extended. Officials cited a drug bust in London in 1968, when Lennon pleaded guilty to possession of “cannabis resin.” Under U.S. law at the time, non-residents faced deportation if “convicted of any law or regulation relating to the illicit possession” of narcotic drugs or marijuana.

Over the next two years, Lennon and Ono endured ongoing government harassment, with FBI director J. Edgar Hoover at times personally involved. Their phone was tapped and their whereabouts closely followed. Lennon would say the pressure helped lead to the temporary breakup of his marriage. The musician left for Los Angeles in 1973 and embarked on what he called his “long weekend” of drinking and drugs, ending with the couple reconciling in 1975.

Meanwhile, musicians and writers and other public figures urged the government to let him stay. Letters of support were signed by everyone from Fred Astaire and Dick Cavett to Saul Bellow and Stevie Wonder. Bob Dylan composed a hand-written note praising John and Yoko as enemies of “this mild dull taste of commercialism” forced on the culture by the “overpowering mass media.”

The Lennons didn’t always help their case. When the couple held their first press conference to discuss the deportation order, the two pulled tissues out of their pockets and declared the birth of a new country, “Nutopia,” a paradise with “no land, no boundaries, no passports, only people.” As representatives of Nutopia, John and Yoko granted themselves diplomatic immunity.

Yoko later apologized, Wildes would recall.

“Leon, you have to understand. We are artists. We have a message,” she told him.

Thanks to Wildes’ ingenuity and the shocking twists of politics in the 1970s, Lennon’s deportation was delayed and ultimately revoked. Wildes found a loophole in the immigration drug law after Lennon told his lawyer that he had been found guilty of possessing hashish, not marijuana (“Hash is much better than marijuana!” Lennon joked). Wildes also highlighted an obscure, unacknowledged government policy of “prosecutorial discretion,” under which officials used varying standards in deciding immigrant cases to pursue.

Meanwhile, the FBI’s targeting of Lennon ended after Nixon’s re-election in 1972, and the INS campaign to deport him began to lose momentum after the growing Watergate scandal led Nixon to resign in August 1974. By October 1975, Mitchell was among many former Nixon officials serving jail time, and Lennon was celebrating an extraordinary week of milestones. On Oct. 7, a federal appeals court judge in New York reversed the deportation order, citing the government’s “secret political grounds.” Two days later, on Lennon’s 35th birthday, Ono gave birth to their son, Sean.

For a final hearing, in July 1976, Wildes brought in Norman Mailer and Gloria Swanson, among others, to testify on Lennon’s behalf, and the INS granted the musician his green card.

“It’s great to be legal again,” Lennon said after the hearing.

The legacy of Lennon’s struggles would endure for decades. When President Barack Obama launched his Deferred Action for Childhood Arrivals program (DACA), for which some children of immigrants were granted temporary relief from deportation, he drew upon reasoning similar to what Wildes had revealed on behalf of Lennon: prosecutorial discretion.

Rock stars, too, were affected. Mick Jagger, who also had been arrested in England on drug charges, was among those who found it easier to travel to the U.S.

“I have in my passport a notation stating that the ineligibility of my visa is withdrawn ‘because of the Lennon precedent’,” Jagger said in a 2005 book, “Memories of John Lennon,” published upon the 25th anniversary’s of Lennon’s murder. “So I have him in my memory every time I enter this country.”

Wildes continued to practice law after his time with Lennon and was an adjunct professor for more than 30 years at the Benjamin N. Cardozo School of Law. His honors included the Edith Lowenstein Memorial Award for excellence in advancing the practice of immigration law and the Elmer Fried Excellence in Teaching Award.

Wildes was married three times, most recently to Alice Goldberg Wildes, and is survived by two children, eight grandchildren and five great-grandchildren.

Descended from European Jews, Wildes grew up in a small Pennsylvania community where he was often the only Jew in his class. He attended Yeshiva College as an undergraduate and became interested in immigration law after working with the Hebrew Immigrant Aid Society in the late 1950s. Wildes published articles in the Cardozo Law Review among other journals and wrote a book on the Lennon case, “John Lennon Vs. the USA,” that came out in 2016.

An opera fan when he was young, he would become fully vested in the Beatles universe, to the point of using “Imagine” as music when a caller to his office was placed on hold. He remained close to Yoko, appeared in the 2006 documentary “The U.S. vs. John Lennon” and even attended some Beatles conventions, among them the Chicago-based Fest for Beatles Fans.

“I spoke there three times, and every time after I spoke, dozens of people came up, shook my hand and thanked me for what I had done for John Lennon,” he told Pennyblackmusic.co.uk in 2017. “And I learned from these wonderful people that it is really something to marvel about and to enjoy this beautiful music of the Beatles. I learned a lot about that kind of music, and now I favor it as well.”