Executive producer John Wells knew he wanted to give the loyal fans of “ER” a few going-away gifts for this, the series’ final season. He would bring back former cast members.

In one case, he had to figure out a way to raise the dead. And he did. Tonight’s episode will feature an appearance by Anthony Edwards, one of the show’s original cast members. He reprises the role of Dr. Mark Greene that he played for 180 episodes over eight seasons.

Greene’s departure in 2002 seemed definitive. The character died after a lengthy battle with brain cancer. But in the world of television, no character is really ever completely dead.

“What happened was I was at home and I got an e-mail from John Wells saying ‘Listen, we’re all sitting here in Hawaii and we’re trying to figure out the last season of ‘ER.’ And we’ve come up with a way of getting Greene back and we’d love to bring everybody back into the show for the audience’s sake,’” Edwards said during a telephone interview from New York. “It makes such perfect sense how they did do it. But I certainly could not have pictured it before.”

All they had to do was turn back the clock. The episode, “Heal Thyself,” features a flashback by Dr. Cate Banfield (Angela Bassett). She had a personal connection to the County General Hospital’s emergency room before signing on for duty this year.

Since leaving the series, Edwards has been selective about the work he has done. He’s preferred to spend more time with his four children and work on several humanitarian projects.

Edwards agreed to return for the lone episode. Just one stipulation: He did not want to be paid.

The offer to be on “ER” came at the same time Edwards was ready to launch a big fundraising campaign to build the largest children’s hospital in Africa. It is a new project to go along with his work with Shoe4Africa.

“So when John Wells asked me, ‘I said I’m happy to, but don’t pay me. Let’s get Warner Brothers to donate to the hospital.’ So in lieu of payment, they gave the hospital $125,000, which Steven Spielberg found out about and he matched. And John Wells kicked in $50,000,” Edwards said. “For me it was really great because they are two things that are really dear to me. The experience that I had for eight years, which certainly changed my life.”

Edwards spent four days filming the episode. “It was actually, you know, everything that you liked about it. None of us got any older. After about a half an hour, it really felt like I’d never left. The same conversations were happening that were happening six years ago, the same dynamics between the crew members, the same jokes,” Edwards said. “And I got to work with Angela Bassett. So how lucky was I?”

During his run on the series, Edwards received four Emmy nominations for outstanding lead actor in a drama series. He also won three Screen Actor’s Guild Awards, the Golden Globe Award for best performance by an actor in a television drama and a People’s Choice Award for favorite male performer in a new television series.

‘ER’

When: 10 tonight

Where: NBC