Spend some time on the website of Tekno Bubbles, and you are sure to encounter Dr. Funk. An aging hippie with wild hair and a penchant for tie-dye, the doctor is a key member of the company's sales force. He greets visitors and describes the company's soap bubbles, which glow when exposed to black light. "We can get you hooked up with some bubbles so you can check them out for yourself," Dr. Funk says as he directs visitors to the site's online store. There, he will suggest complementary items that can be found on the site, such as bubble-blowing machines and remote-controlled timers.

Dr. Funk doesn't work in Tekno Bubbles's St. Louis office -- or, for that matter, in any physical location. He operates exclusively online. That's because Dr. Funk is an avatar, an animated online character used to represent a person or brand.

Originally confined to virtual worlds such as Second Life, avatars are increasingly making their way onto commercial websites as businesses seek new ways to interact with customers. By performing tasks such as greeting visitors and fulfilling orders, avatars can enhance a website's sales and service, reduce the costs of live customer support -- and, as with Dr. Funk, provide a sense of personality and playfulness.

Adding an avatar is surprisingly inexpensive. The simplest takes as little as 30 minutes to create and costs less than $10 a month to maintain. SitePal, a service of the interactive marketing firm Oddcast, offers a gallery of more than 250 stock avatars, with options for customizing their facial features, wardrobe, and background scenery. Other companies, such as CodeBaby, VirtuOz, and Next IT, design custom avatars for clients. Most avatars can be programmed to deliver specific messages about a company's product or services. Some use text-to-speech technology to convert written scripts into spoken messages. For a more natural-sounding voice, you can record your own greetings to visitors. Many providers also offer the option of hiring professional talent to serve as your avatar's voice. (Dr. Funk, for his part, sounds as if he would get along well with Tommy Chong.)

Dr. Funk made his debut on teknobubbles.com in November. Since then, online sales have increased from 30 percent of Tekno Bubbles's grosses to 50 percent. The company has also begun using images of Dr. Funk in offline promotions, including trade show displays. "He's able to touch the market we want to touch," says owner John Reider. "I'm 45 years old, and I've lost most of my hair. I couldn't do the same job he could."

Still, avatars aren't for everyone. They tend to work best for companies whose websites are the main venue for purchases, lead gathering, or customer assistance, says Mark Gaydos, VirtuOz's vice president of worldwide marketing. They are also better suited for companies that sell to consumers rather than to other businesses.

Even if your site proves an ideal fit for an animated helper, it's important to heed certain guidelines to ensure that your avatar serves as a helpful guide -- instead of an unwelcome, or even creepy, nuisance. Animations that abruptly leap from a page or bear too much resemblance to a live person tend to turn visitors away. Avatars make the most impact, says Yujin Sohn, Oddcast's senior director of marketing, when used to encourage some kind of action on the part of the customer, such as filling out a contact form. As with videos, it is best to keep their messages short, no longer than 30 seconds each. They should also have an Off button for visitors who prefer to browse without assistance.

By following these rules of thumb, businesses can make avatars their sites' leading attractions. Reider says he often receives inquiries about Dr. Funk. "He's an old bubble hippie," he says. "Who's not going to love him?"