When Jim Parsons was cast in Netflix’s limited series “Hollywood” as Henry Willson, the real-life agent best known for shepherding Rock Hudson to mega-stardom, the multiple Emmy-winning actor immediately turned to Google. While he couldn’t find any contemporaneous video of Willson, there were at least plenty of photographs. Looking at them, Parsons was struck with an immediate concern.

“My first thing was, could I look different at all?” he says.

Similar to several other supporting performers now nominated for taking on roles based on real people, however, Parsons’ transformation into Willson was ultimately a subtle one. He utilized understated false teeth, wore color contacts to change his eyes from blue to brown, and changed his hair just slightly to suggest that Willson was wearing a toupee.

“In several different shots, you can see his scalp from the back,” says Parsons. “That being said, a lot of it was in preparation for a scene that ended up never coming: He was going to take his toupee off, and we would reveal his bald head.”

Willson died in 1978, so Parsons says his biggest resource was the biography “The Man Who Invented Rock Hudson” by former Variety editor Robert Hofler. “That really became my bible.”

By contrast, early in her career, Helena Bonham Carter actually met Princess Margaret, the British royal she played on the third season of Netflix’s “The Crown.” When she got the role for the show’s third season, Bonham Carter also spoke extensively with Margaret’s friends and contemporaries, including her lady-in-waiting, who informed Bonham Carter that the princess’ life wasn’t as glamorous as the show makes it seem.

“They don’t have unlimited money, and the real Margaret, who is quite different from our Margaret, was on a much tighter budget,” says Bonham Carter. “Even the queen mother was giving her money for clothes. But in our ‘Crown,’ we barely repeat a costume.”

Along with her own fact-finding, Bonham Carter was thrilled with the exhaustive research done by the show’s props department. “Right at the beginning of the season, you walk into this hangar and they’ve laid out all these props, which are basically a portrait of your character in objects,” she says. “I had this fantastic Cartier lighter — proper gold, heavy. It was important to have that authentic and heavy object, because with Margaret the key to everything was there was a weight to her, and deliberateness.”

As for executing her physical resemblance to Margaret, Bonham Carter simply says, “I’ve never been so grateful to a wig in my life.”

For her performance as feminist trailblazer Betty Friedan on FX on Hulu’s limited series “Mrs. America,” Tracey Ullman also used not much more than a wig and some makeup to embody the role. Although she initially entertained a more extensive transformation, using the kind of facial prosthetics she’s employed for decades on her own shows, mainly to try to re-create Friedan’s distinctive eyes, ultimately, it didn’t jibe with the show’s overall approach.

“I was so liberated not to have anything, actually. I really enjoyed it,” she says.

Instead, Ullman deployed her uncanny facility for vocal mimicry to capture Friedan’s low Midwestern rasp. “It’s such an educated, of-its-time voice,” she says. “Somebody who went to Smith and had an education and liberal parents — political, Jewish, Midwest.”

Similarly, “Mrs. America’s” Uzo Aduba used not much more than a large beehive wig to personify Rep. Shirley Chisholm, who was the first Black woman to run for president of the United States in 1972. In her research, Aduba came to understand that Chisholm used the wig for a critical political function as much for making a fashion statement.

“She was really tiny,” says Aduba. “If she didn’t wear something this size, she would be invisible.”

Unlike Ullman, however, Aduba elected to dial back imitating Chisholm’s voice — specifically her slight speech impediment, save for one moment when the character is seen speaking on TV. “I didn’t want it to be more pronounced than it was,” Aduba says. “It wasn’t distracting [in real life], but if I’m doing it, it becomes distracting, and I’m actually not being true to Shirley Chisholm.”

The biggest revelation in Aduba’s research was a moment in the documentary “Chisholm ’72: Unbought and Unbossed” in which, after finally conceding defeat at the Democratic National Convention, the candidate openly wept in front of her supporters.

“When you’re dealing with people who are standing in spaces that have never been held by people like themselves, it’s not just being able to capture the candidate Shirley Chisholm, it’s actually trying to find the human who’s carrying the weight of the world with her,” she says.

Like Aduba, “Mrs. America” co-star Margo Martindale — who plays Rep. Bella Abzug — had never once taken on a major role based on a historical figure.

“I found that extremely scary and I felt unbelievably responsible,” says Martindale.

Abzug represented parts of New York City in the 1970s when Martindale first started living there, so she was already familiar with Abzug’s career and persona. But the actor still dove deep into researching Abzug’s life and approach to politics, including when she clashed with Chisholm during the ’72 campaign.

“She was on fire about things, but she always used facts to support it,” Martindale says of Abzug. “She wasn’t mean; she was outspoken — and there’s a very different way to do that.”

Some of Martindale’s research ended up not applying directly. “She could play a lot of instruments, and I decided that I couldn’t really put that in there,” Martindale says with a laugh.

But ultimately, she hoped it all informed her performance.

“Honestly, I’ve never worked so hard in my life on a role,” she says. “You fill yourself up with it all, and hope it comes out organically.”

Will Thorne contributed to this report.