Oprah's last show marks a milestone in an iconic career, one that has been wildly successful beyond imagination.

Oprah Winfrey is easily the most liked woman in the US, certainly the most successful African-American female entrepreneur in US history, and a major agenda-setter in society for the last 25 years.

Oprah achieved that level of success because she was good.

Eschewing tabloid sensationalism, The Oprah Winfrey Show brought out the good in the world and encouraged viewers to do better in their lives. It was also highly entertaining and interesting.

Oprah wasn't just an ideologue or saint.

She had an uncanning sense for entertainment (she even made classic books interesting) and self-promotion and sold her brand hard at every opportunity. She was also mindful of giving people what they wanted and striking a cord with the public psyche.

But she did it all in a respectable and uplifting way.

One key advantage to her approach was legitimacy. Legitimacy meant her show can be talked about in polite company. It also meant the biggest stars had no worries going on her show and associating with her brand.

In fact, Oprah - and her Oprah effect - was the force that set the agenda and made or broke public careers.

Oprah finished out her last show in a sincere and dignified fashion. She gave her thanks and reiterated her feel-good message of love for all.

She will now focus more on her own cable network, so her influence could actually expand to greater heights in the long-term. Still, The Oprah Winfrey Show was an irreplaceable cultural icon in the last 25 years and its ending marks an exit of a force for good - one that the public needed and her loyal fans will deeply miss.