Alleged Boston gang boss James "Whitey" Bulger has appeared in federal court in Los Angeles and been remanded to Massachusetts to face charges, following his arrest early on Thursday.
Mr Bulger, 81, appeared with girlfriend Catherine Greig, 60, and waived his right to contest the transfer.
Mr Bulger was on the FBI's "Ten Most Wanted" list, and is accused of involvement in 19 murders.
He was the inspiration for the Martin Scorsese film "The Departed".
Mr Bulger, who officials say spent 16 years on the run, was played by Jack Nicholson in a movie that won four Oscars in 2007.
Mr Bulger is accused of running the Winter Hill gang in the 1970s and 1980s.
Mr Bulger held court documents against his chest when he appeared before Magistrate Judge John McDermott, saying he understood the charges against him.
He then smiled as he was led away by law enforcement agents.
Mr Bulger and Ms Greig's arrest in Santa Monica, California, came days after the FBI began airing 30-second public service announcements, focusing on Ms Greig.
They specifically targeted programmes watched by women of Ms Greig's age, and urged them to keep an eye out for her.
On Thursday, officials said the publicity campaign had generated the tip that led to their discovery in Santa Monica, where the couple had been living under the names Charles and Carol Gasko.
After receiving the tip about 1600 local time (2000 GMT) on Wednesday, federal agents began watching the suspected fugitives, eventually luring Mr Bulger out of the Santa Monica flat through a ruse.
After confirming his identity, they arrested him without incident, then entered the apartment and arrested Ms Greig, officials said on Thursday.
Inside the apartment agents found "a variety of weapons - firearms" and "a very substantial amount of cash", FBI Special Agent in Charge of the Boston Division Richard Deslauriers told reporters.
The pair now face extradition to Boston to face federal charges.
The Winter Hill gang was a largely Irish-American mob that ran loan-sharking, gambling and drug rackets in the Boston area.
Mr Bulger disappeared shortly before he was due to be arrested in connection with 21 killings and racketeering.
Following his disappearance, it emerged he had been a long-time FBI informant who turned in rival gangsters.
The revelations left the FBI fighting accusations that it had long been turning a blind eye to the alleged crimes of James Bulger and the Winter Hill gang.