Apple posted two ads featuring Malkovich to its official YouTube channel on Wednesday.
In "Joke," Malkovich leans back in a chair querying Siri while having a drink and listening to opera music. His requests contain just one word: "weather," "evening," "linguica" and "joke."
In response to the request for a joke, Siri says, "Two iPhones walk into a bar. I forget the rest." Malkovich then finds the joke hilarious and tells Siri, "That's funny."
"Was it something I said?" Siri asks, to which Malkovich replies, "Yes, it was."
The second ad, "Life," shows Malkovich in the same chair staring off into space before saying the word "life" to Siri.
"Try and be nice to people, avoid eating fat, read a good book every now and then, get some walking in, and try to live together in peace and harmony with people of all creeds and nations," Siri responds.
"That's pretty spectacular advice, actually," Malkovich says. "Thank you, I enjoyed this chat immensely, you are very eloquent."
Last month, Apple ads featuring Samuel L. Jackson starring Zooey Deschanel began showing on TV. Jackson used Siri to help prepare a date night, while Deschanel searched for tomato soup delivery on a rainy day.
Previous advertisements for the iPhone 4S have also centered largely around Siri. Two ads that aired in February highlighted the feature's usefulness on a cross-country road trip and in learning guitar.
Those ads actually turned out to be controversial. Class-action lawsuits filed this spring allege that they constitute false advertising because Siri doesn't work as depicted in the commercials. Apple responded earlier this month by claiming that plaintiffs' accusations are overly "vague" and lack standing.