Flo made her 100th ad appearance this week with a new campaign from Progressive agency-of-record Arnold Worldwide.

Over the past seven years, Flo has donned many hats. She evolved from her humble beginnings as a cashier into a love interest, a reality star and an insurance pusher; she made friends and enemies. She even gave audiences a glimpse into her youth. Such approaches have allowed the character to stay relevant with consumers through 100 ads and counting, but CMO Jeff Charney said it's her relatable-nature that gives her staying power.

"She was authentic and real," said Mr. Charney. "She was different than anything else in the industry… an industry that is literally an arms race right now."

Insurance companies have been warring to become top of mind with consumers. Allstate's "Mayhem" campaign was born out of this battle. "We wanted to kick Flo's ass," said Nina Abnee, exec VP at Allstate's agency Leo Burnett.

In Flo's one-hundredth ad, which went wide earlier this week, we meet Flo's bickering family. Stephanie Courtney, the actress who stars as Flo, plays all six family members in the spot -- mom, dad, brother, sister, grandpa and Flo. The ad was designed to build a deeper connection to the character, tap into a relatable moment and showcase the campaign's range, which often includes improvisation and supporting characters.

It took 12 hours of makeup to transform Ms. Courtney into Flo's family. On set, she acted opposite metal sticks that served as placeholders while surrounded by cameras. The push was scripted but left opportunities for ad libbing, which created some of Mr. Charney's favorite lines, like "I've got the meat sweats."

"We were trying to go back to our roots of improvisational comedy," said Mr. Charney.

Stealing the spotlight from the 'Superstore'
It was a bit of improv that made Flo a star, following her 2008 debut.

Progressive's initial goal for the campaign was to make shopping for insurance a pleasant experience -- a tall order. To do that, the marketer built the "Superstore," which was a clean, open market where insurance was shoppable and sales people, like Flo, offered help.

"The role of the superstore was to make the intangible tangible," said Progressive CEO Glenn Renwick.

Flo appeared as a cashier in the first spot, called "Checkout." The script also encouraged ad libbing and Ms. Courtney broke through with the line, "wow, I say it louder," stealing the spotlight from the "Superstore."

"Flo was an accident," said Mr. Charney. "That line was really what made it powerful."

Ms. Courtney was a front-runner for the role of Flo early on because she was "good on her toes," said Nichole Brown, a marketing specialist at Progressive who watched Ms. Courtney's audition tape in 2007.

As the campaign evolved, the concept of the "Superstore" surrounded Flo with characters to play off and offered other opportunities to expand Flo's story.

"This thing could go on a lot longer because it's a bigger concept -- the store -- with an amazing character," said Mr. Charney.

Combatting Flo-fatigue
Mr. Charney joined Progressive from Aflac in November 2010 when consumers started tiring of Flo. Earnings growth slowed that year -- gains fell to 2%, compared with 3% in 2009 -- according to annual reports. That was followed by Flo-fatigue, as the company calls it, which climbed in 2011. Progressive was experimenting with supporting characters like the Rivals, a pair of driving foes, and the Messenger, the campaign's mustachioed-hero, to reengage audiences. When Mr. Charney arrived he took things a step further -- moving Flo out of the store for a date.

"'The Best Day' was our first wink that people crush a little bit on Flo," said Mr. Charney, who refers to spots as episodes. "'The Best Day' gave that a little more edge and showed that we could change with the time."

A personal affinity for TV inspired Mr. Charney to revamp the "Superstore" campaign, acting as a TV network and treating the push like a sitcom. The new approach included flashbacks to Flo's youth, ensemble cast members like Flo's sidekick, Jamie, and Pickles the dog, set changes, alternate worlds, and a spin-off starring "The Box."

"We view new ad briefings through the eyes of a Hollywood executive that's tasked with keeping shows fresh and leveraging the strength of existing programming to bring new shows to market," said Mr. Charney, who said he looks to classic sitcoms like "All in the Family" and "Good Times" for ideas.

Progressive also developed an in-house media team to connect the brand to more channels. The company spent $587 million on advertising last year, up 17% from 2012, according to the Ad Age Datacenter. It is the country's 70th largest advertiser.

"We buy our media inside the company, which makes me, as a network executive, really strong," said Mr. Charney. "I have hundreds of channels to put my content in the right context."

Progressive's revenues grew steadily after the network strategy was put in place. It reported $18.2 billion in revenues in 2013, up 15% from 2011, according to annual reports.

One hundred ads in, Flo still has a strong fan base. People even dress up as the Progressive girl for Halloween. The $40 costume comes with a perky wig, apron, nametag and insurance box.

Progressive is celebrating Flo's milestone with five minutes of new content that will roll out during the month, dubbed Flovember, which includes the 100th ad. Mr. Charney declined to comment on the budget. But said the campaign "is really the network showing its full muscle."

Flo may not have another hundred ads left in her, but Progressive will keep working with the character.

"We will continue to evolve Flo and hopefully as Flo evolves, the audience will continue to evolve with her," said Mr. Renwick.

Flo's Top Five Spots
Flo has been everything from cashier to love interest to reality star in order to stay fresh for consumers. Recently, Progressive took a more targeted approach to the character, using metrics to see what works for consumers. Below are Flo's five most effective spots, based on customer responses, new prospects, sales and other factors measured by Progressive.

#1 "Heist," March 2014

#2 "Empowered," January 2013

#3 "Peer Pressure," January 2013

#4 "Reality Flo," March 2014

#5 "Secret Weapon," June 2013