Guillermo's broken English (characterized most clearly with his constant pronunciation of the show's host as "Yim-ee") coupled with his affable likability and Teddy Bear-like quality have earned him as high a profile as any supporting personality on the show. Guillermo has taken over main red-carpet interviewing duties from Kimmel's original choice for such events, "Uncle Frank" Potenza.
Guillermo's signature segment is "Guillermo's Hollywood Roundup", in which Guillermo, dressed in a cowboy outfit and pretending to twirl a special effect operated lasso, makes mockery of entertainment news shows featured widely on television. From outside the theater and standing next to his West Coast Customs-made "Guillermobile", he'll answer inquires directed at him from Kimmel about the latest tabloid stories by simply taking a rack of tabloid magazines that the "Guillermobile" has been fitted with and attempting to interpret the stories in usually an unintentionally and amusingly mis-translated way.
Another popular and recurring bit is announcing that Guillermo has a role in a current or recent major motion picture release and showing a clip of an at-first familiar trailer for said movie with Guillermo humorously edited in, his appearance often made-up to resemble a character in the movie. One of the more popular ones had been when he impersonated Matt Damon's character of Jason Bourne in The Bourne Ultimatum by responding when asked to be named, "I am Yay-son...the Bourne..Identity." A physical fight between Guillermo and Matt Damon's actual character ensued. He also has recently been featured in a segment where he quizzes the reigning junior spelling bee champion on a series of words. He typically mispronouces these words hilariously, such as pronouncing "ginger" as "yee-yer," and "vapid" as "bah-pee."