James O'Keefe may not yet be a household name, but his outlandish political pranks have certainly caused a splash. The 26-year-old conservative activist first came to prominence with a video hoax that ended up crippling social-services group ACORN. Now he's back with an attack on NPR that has resulted in the resignation of the network's chief executive. Here, a rundown of his 5 biggest hoaxes:

1. Catching an NPR executive bashing Tea Partiers
O'Keefe orchestrated this week's video ambush of NPR executive Ron Schiller, who was caught on tape lambasting Tea Party conservatives as "seriously racist" people. Two "undercover O'Keefe lackeys" posed as representatives of a Muslim education charity, and reportedly offered to give NPR a $5 million donation. The dust still hasn't settled, but NPR chief executive Vivian Schiller (no relation) has already resigned from her post. O'Keefe's "fraternity-like tactics" went too far this time, says Leslie Marshall at U.S. News & World Report. "Taping anyone without their consent is illegal," and I think Ron Schiller should sue "big brother O'Keefe."

2. Getting ACORN to help "ladies of the night"
O'Keefe first came to prominence in September 2009 with a sting operation on the Association of Community Organizations for Reform Now (ACORN). The young prankster and a colleague, dressed as a pimp and a prostitute, visited ACORN offices in several cities seeking advice on securing a housing loan. The damaging responses — "honesty is not going to get you the house," one ACORN official was recorded saying — led to the end of federal funding for the community organization, and it filed for bankruptcy the following year. "That 20-minute video ruined 40 years of good work," said an ACORN official. An investigation into the tapes later found they had been selectively edited "to the point of dishonesty."

3. Trying to tamper with a Democratic senator's phone
Not all of O'Keefe's pranks have been successful. The activist was arrested in January 2010 after breaking into the New Orleans office of Sen. Mary Landrieu (D-La.), in an apparent attempt to interfere with the building's telephone lines. O'Keefe and three accomplices were later given three years probation and a fine for entering federal property under false pretenses. Some of O'Keefe's former fans expressed distaste at his tactics. Glenn Beck said he had entered "Watergate territory."

4. Attempting to humiliate CNN
Undeterred by his arrest in Louisiana, O'Keefe continued to try to embarrass those whom he sees as shills for the left. In September 2010, CNN revealed O'Keefe was plotting to embarrass CNN correspondent Abbie Boudreau by luring her onto a boat filled with "sexually explicit props" and filming her reaction. CNN smelled a rat, and reported O'Keefe's involvement with the failed stunt. This time, even the conservative blogosphere reacted with disdain. Exposing media bias with a video camera is one thing, said Caleb Howe at RedState, but "luring a lone female reporter to a remote location" in an attempt to cause her "discomfort and fear"? That's just "despicable."

5. Exposing teachers unions in New Jersey
O'Keefe returned at the end of 2010 with a secret video filmed in New Jersey, which purported to show unionized teachers admitting how hard it was to fire a tenured teacher. In one of the tapes, teacher Alissa Ploshnick says one of her colleagues called a pupil a "nigger" without being canned. Still, the video, said Bob Braun at the New Jersey Star-Ledger, was a "phony expose of nothing but the cynicism of ideologically driven pseudo-journalists."