Rosie is a blue-collar version of Martha Stewart, outgoing, loud, sometimes coarse and always opinionated. She's also a comic.
On the other hand Calista is a quiet-spoken, ladylike, ephemeral and somewhat shy heroine of the "Ally McBeal" series in which she plays an elfin attorney who also leads an imaginary life.
O'Donnell is a rough-hewn, heavyset Irish-American from Long Island, somewhat tough and swaggering but with a heart of gold. She is a self-confessed lesbian who lives with her lover who is expecting a baby.
Flockhart is as slender as a rail, diminutive and shy, a native midwesterner from Freeport, Ill. who was educated at Rutgers University. She is unmarried but involved romantically with movie star Harrison Ford.
Rosie is 40; Calista is 37.
Doubtless many viewers, especially women, regularly tuned in both "The Rosie O'Donnell Show" and "Ally McBeal" and will regret their departures.
O'Donnell's show reflected the host's own rough-and-tumble, in-your-face confrontations with which many women could connect. She was scrappy, sarcastic, funny and always sure of herself.
She lost some viewers with her aggressive attitude toward some of her guests, notably Tom Selleck who took issue with her when she chose to discuss his politics.
Flockhart, on the other hand, crawled inside her on-screen persona, Ally McBeal, a somewhat timorous attorney who indulged her fantasies, which would be totally foreign to O'Donnell.
Rosie has vastly more experience as a performer than Calista, having appeared in 35 movies and TV shows.
Among her films are "A League of Their Own" (1992), "Harriet the Spy" (1996), "Sleepless in Seattle" (1993) and "Beautiful Girls" (1996) -- don't ask.
Calista's half-dozen movies include "Telling Lies in America (1997), "The Birdcage" (1996), "Drunks" (1995) and "Milk and Money " (1997).
Neither actress would qualify as a movie star, but both are TV stars who have been extraordinarily publicized as in-the-spotlight personalities.
Those intrigued by Flockhart's name should know she was named for her great-grandmother and that "Calista" means "most beautiful" in Greek.
Like Rosie, she has an adopted child, a son named Liam.
O'Donnell, who says she will never have biological children because of a family history of alcoholism and cancer, has adopted three children: Parker, Chelsea and Blake.
Much of Rosie's career is based on her strong personality, outspoken amiability and raucous sense of humor. She seeks the limelight and has the self-confidence to become the life of any party.
Contrarily, Calista is retiring and self-effacing. Although she was a high school cheerleader, she is essentially an introvert.
Some of Flockhart's best work has been in the theater, including her role of Laura in Tennessee Williams' "The Glass Menagerie" on Broadway.
Rosie's on-stage background is as a stand-up comedienne where her robust humor evoked a large fan following and won $20,000 on the "Star Search" show.
Very much a private person, Calista conducts few interviews and is averse to discussing her private life, as is boyfriend Ford. Flockhart inadvertently made news a year and a half ago when she collapsed on the set of her show, suffering dehydration and exhaustion. Friends denied she was suffering from anorexia or bulimia.
No one would ever believe that hefty Rosie ever fell prey to either problem.
There is something of the waif in Calista's appearance that would be totally out of place with the energetic, kinetic Rosie.
There also is something of the conservative Victorian female in Calista that is utterly foreign to the effervescent Rosie who feels right at home in the spotlight.
Rosie and Calista are at opposite ends of American womanhood, representing two extremities. Calista is ultra feminine while Rosie represents the eternal tomboy.
Both women share a unique niche in the current scene of American women in transit, post-feminine revolution. Both might appear to be extremists in that regard.
They are the yin and yang of the feminist movement, polar opposites, representative of show business bookends.
In-between these extremes fall most of Hollywood's female performers: Julia Roberts, Sharon Stone, Michelle Pfeiffer, Renee Zellweger, Ellen Degereres, Sandra Bullock, Nicole Kidman, Jennifer Aniston and all the others.
It would be interesting were Rosie and Calista to be interviewed together on a neutral show, say, Letterman or Leno, to see how these two very different entertainers feel about their lost shows and the challenges and opportunities they now face.