Guest actor casting in today’s increasingly rich landscape of television has evolved far beyond the days of glorified cameos, slumming stars or celebrities doing friendly favors. And the myriad ways that series and actors — from rising stars to A-listers — come together can result in moments of pure gold, on screen and at awards ceremonies.

Ann-Margret took a guest role on Netflix’s “The Kominsky Method” to shake off the grief she felt after the passing of her husband. “All of a sudden I get this call from [Alan] Arkin and he said, ‘You’ve got to get back to work!’” the screen icon recalls. Arkin pitched her to series creator Chuck Lorre to play the woman pursuing his recently widowed character, and they were soon sharing scenes together. “At the very end I said to him, ‘You were right.’”

Casting director Jen Euston, who’s found talent for Jenji Kohan’s “GLOW” and “Orange Is the New Black,” says working with pay networks such as HBO and Netflix often allows greater latitude to find fresh faces for guest roles.

“Those kinds of places don’t make me say we have to get a ‘name’ for this role — let’s get the best actor for the role,” she says.

Several of her guest role discoveries, including Uzo Aduba, were elevated to regular status after making a major impression on both viewers and awards voters. “People called about anybody they saw on ‘Orange,’ like, ‘Where’d you find this person?’ And they think I did street casting for a lot of the girls,” says Euston. “They were so talented and were so real, but they were so trained. It’s a pressure to always have to be right, but the validation comes from seeing these people soar.”

Over on broadcast, stunt casting can be more important to ensuring additional eyes on a project or just adding an air of an extra special nature to a specific episode or arc — but it isn’t the end-all-be-all.

When, in the third season of “This Is Us,” it came time to cast the role of Beth’s (Susan Kelechi Watson) mom, “right from the beginning,” producers said to casting director Josh Einsohn, “Wouldn’t it be great if we could get Phylicia Rashad?”

Rashad had known Watson as a college student and they’d performed together on stage — Watson, too, lobbied for Rashad. Since they already had a history, Rashad admits there was a feeling of “I could almost be” Watson’s mother. But, she says, the challenge of the part came from wanting “to be as good as everybody else there.”

“When we were on set and I was looking at Susan I said, ‘OK, Phylicia, buck up. You’ve got to be as good as the people you’re working with.’ And that’s a challenge that I always welcome.”

For the role of Nicky, Jack’s (Milo Ventimiglia) estranged brother who was presumed to have died in the Vietnam War, Einsohn faced different challenges: casting two actors to play the man, rather than using prosthetics and makeup to age one person as is customary with the series regulars. For the Vietnam-era version of Nicky, the show cast Michael Angarano. Later in the season’s run, for the present-day version, Griffin Dunne was hired.

“It’s not just about matching a look. It’s also about matching an energy and a performance and the quality that’s got to work for the character,” Einsohn says. “To find somebody who has all the skills and the energy and looked like Michael was one of the more nerve-wracking challenges we’ve had. Griffin was brought to our attention at the same time that we thought of it internally. You just felt a collective light bulb go off: ‘Ah, yes, that’s perfect.’”

Dunne and Angarano had previously played father and son in the film “Snow Angels,” but had little time to compare notes on the shared character.

“What’s amazing was how closely [our performances] lined up anyway,” Dunne says. “So many people thought that we must have rehearsed, but in fact, we didn’t have time to.”

As the number of shows continue to bloom and actors are locked down for longer periods, fresh opportunities to discover and introduce new names are popping up, even on broadcast. Khalilah Joi was relatively unknown outside industry circles until she landed a role as a sexual-assault victim on an episode of “Grey’s Anatomy.” It was a role out of the blue after two years of auditioning for five different parts on the series.

“My actor friends always tell each other it’s not necessarily about booking a role, it’s about making a fan in the room,” says Joi. “Going in, doing your best and doing work that a casting director is going to remember and then bring you back for something else. They kept bringing me back time and time again. It just eventually all worked out.”

Julie Ashton-Barson, who has cast “Will & Grace” since its reboot began, balances the show’s tradition of inviting well-known guest performers — this season’s additions included Matt Bomer, Jane Lynch, Andrew Rannells, Vanessa Bayer and Aya Cash — and showcasing new discoveries, including Brian Jordan Alvarez, who plays Jack’s husband, Estefan.

“I saw Brian in a diversity showcase and always had him in the back of my mind for something special,” says Ashton-Barson. “He started off doing one episode and he was such a hit that we brought him back again and again and again. That you can help really creatively cast a brand new part that’s written so well with somebody that good has been very gratifying.”

For some, guest starring roles can be a chance to go outside one’s usual character type or to play on a new platform. Such creative opportunities were a major motivation for Ginnifer Goodwin signing onto an episode of “The Twilight Zone” reboot.

“There’s more room to take risks, there’s more opportunities for creativity,” she says. “Because there was no worry about what the effect on the audience [would be], I [didn’t] have to be likable; I didn’t have to be obviously pleasing any advertisers in this particular situation. It just felt very free. I got 10 days to just explore this character, and she’s the whole story. It was like doing theater for a couple of weeks.”