Will Ferrell, known for his comedic roles in films like "Anchorman" and "Elf," brought his unique brand of comedy to "The Office" in Season 7, playing Deangelo Vickers, Michael Scott's temporary replacement as regional manager. Ferrell's character was a hit with fans, and his comedic timing added a new dimension to the show's humor. His character was quirky and unpredictable, much like Ferrell's other roles, making his episodes some of the most memorable in the series.

Before she became a five-time Academy Award nominee, Amy Adams appeared in "The Office" as Katy, a handbag saleswoman who becomes a love interest for Jim. Her character added an interesting dynamic to the office, creating a love triangle with Pam. Adams' portrayal of Katy showcased her versatility as an actress, as she was able to bring depth and complexity to a relatively minor role.

Roseanne Barr, best known for her role in the sitcom "Roseanne," played Carla Fern, Andy's new talent agent, in two episodes of Season 9. Her character added a touch of Hollywood glamour to the Scranton office. Barr's comedic timing and distinctive voice made her a memorable addition to the show, and her character's interactions with Andy provided some hilarious moments.

Two-time Academy Award nominee Joan Cusack made a memorable appearance in the show's finale as Erin's biological mother, who had given her up due to her and her husband's work as puppeteers. Cusack's emotional performance added depth to the finale, and her reunion with Erin was one of the most touching moments in the series.

Veteran actor Ed Begley Jr., known for his roles in shows like "St. Elsewhere" and "Arrested Development," also appeared in the finale alongside Joan Cusack, playing Erin's biological father. His character's reunion with Erin provided a heartwarming conclusion to her storyline, and Begley's performance added an extra layer of emotional depth to the episode.

Late-night talk show host Conan O'Brien made a brief cameo as himself in a Season 2 episode of "The Office." His appearance was a humorous nod to his status as a fellow NBC star, and his interaction with Michael, who mistook another woman for Tina Fey, was a hilarious moment in the series.

Ricky Gervais, the creator and star of the original British version of "The Office," made a couple of cameo appearances as his character David Brent. His interactions with Michael Scott were a delight for fans of both series, and his presence served as a humorous reminder of the show's origins.

Before her rise to fame with the "Fifty Shades" series, Dakota Johnson appeared in the final episode of "The Office" as one of the new hires Dwight made as regional manager. Johnson's character, while minor, added a fresh dynamic to the office in the series' final episodes.

Warren Buffett, one of the world's most successful investors, made a surprise appearance as an interviewee for the role of regional manager. His cameo was a humorous nod to his real-life status as a business magnate, and his character's frugal negotiation over a potential salary was a clever in-joke about his well-known value-oriented investment style.

Bob Odenkirk, best known for his role in "Better Call Saul," appeared in Season 9 as the manager of a real estate office in Philadelphia where Pam was interviewing for a job. His character, Mark, was eerily similar to Michael Scott, providing a humorous "what if" scenario for Pam and the viewers. Odenkirk's comedic timing and ability to play quirky characters made him a perfect fit for the show.

"The Sopranos" star Michael Imperioli made an appearance in Season 9 as Sensei Billy, Dwight's new sensei who finally bestowed upon him a black belt. Imperioli's character added a new layer to Dwight's storyline, and his serious demeanor provided a humorous contrast to the show's usual comedic tone.

Melissa Rauch, known for her role as Bernadette in "The Big Bang Theory," played a new mom in Season 6 who shared a hospital room with Pam. Her character, Cathy, was a relatable figure for Pam as they both navigated the challenges of motherhood, and Rauch's comedic skills made her a memorable guest star.

"GLEE" star Kevin McHale showed up in Season 4 as the pizza delivery boy that Michael temporarily kidnapped. His character's ordeal at the hands of Michael and Dwight was one of the show's most absurd and hilarious scenarios, and McHale's performance added to the comedic chaos of the episode.

Maura Tierney, known for her roles in "ER" and "The Affair," played Robert California's wife who was looking for a job in the Scranton branch in a Season 8 episode. Her character's interactions with the office staff, particularly her awkward interview with Andy, provided some of the season's most cringe-worthy and hilarious moments.

The former Phillies slugger showed up in Season 9 as a potential client Jim and Daryl were trying to lure to their company. His appearance was a fun surprise for sports fans, and his character's interactions with Jim and Daryl provided some humorous moments as they tried to win him over.

Before he became known as young Bruce Wayne on "Gotham," David Mazouz appeared in the Halloween episode of Season 8 of "The Office." His character, Bert California, was the son of the enigmatic Robert California, and Mazouz's performance added a touch of youthful innocence to the show.

Comedic actor Will Arnett, known for his roles in "Arrested Development" and "Bojack Horseman," appeared in Season 7 as an interviewee for the regional manager position. His character, Fred Henry, was tight-lipped about his plans for the company, adding a layer of mystery and humor to the interview process.

Comedy legend Jim Carrey made a brief but memorable appearance as a quirky interviewee for the regional manager position. His character's obsession with the Finger Lakes became a running joke, and Carrey's comedic skills made his cameo a highlight of the episode.

Basketball legend Julius Erving, also known as Dr. J, appeared in Season 9 as an Athlead client. His appearance was a fun surprise for sports fans, and his interactions with Jim and Daryl added a touch of real-world fame to the show's fictional universe.

Former NFL player Jerome Bettis, also known as 'The Bus,' made a cameo as himself, signing autographs and turning down an invitation to Michael's hotel party. His appearance added a touch of sports star power to the show, and his interaction with Michael provided some humorous moments.

Comedian Tim Meadows, known for his stint on "Saturday Night Live," played Christian, a representative from Lackawanna County who met with Jan and Michael at Chili's to discuss the paper needs for the county. Meadows' comedic timing and his character's interactions with Michael and Jan made for some of the show's most memorable moments.

Emmy-winning actor Ray Romano, best known for his role in "Everybody Loves Raymond," appeared in Season 7 as an applicant for the regional manager position. His character, Merv Bronte, found his efforts sabotaged by Robert California, and Romano's portrayal of a down-on-his-luck job applicant added a touch of humor and relatability to the episode.

"American Idol" runner-up Clay Aiken made a cameo as a judge for the show 'America's Next A Capella Sensation.' His appearance was a fun surprise for fans of the singer, and his character's unimpressed reaction to Andy's performance provided some humorous moments.

Singer Josh Groban appeared in episodes in both Season 8 and Season 9 as Andy's younger brother. His character's privileged background and successful music career provided a contrast to Andy's struggles, and Groban's performance added a touch of real-world fame to the show.