When Americans first saw PBS’ “Sherlock” series in 2010, they were beguiled by Benedict Cumberbatch as a Sherlock Holmes who managed to be both snarkily contemporary and true to Sir Arthur Conan Doyle’s original character. But those of us who’ve been hanging tough with PBS’ “Masterpiece” over the years are old friends with Cumby’s talent — and his cartoony name. Before “Sherlock” and his noted appearances in films including “Atonement” and “Tinker Tailor Soldier Spy,” he had the starring role in a fine 2005 “Masterpiece” miniseries called “To the Ends of the Earth.” To get all first-gradery about it, yeah, we knew him first.

A lot of great older actors, such as Michael Gambon, Judi Dench, Imelda Staunton, Charles Dance, Maggie Smith, and Derek Jacobi, continue to bring their decades of experience to “Masterpiece.” But the series is also a launching pad for up and comers, from Emily Blunt to Rose Byrne. Here are a few now-known British actors whom American “Masterpiece” fans saw first.

Benedict Cumberbatch

Known for: “Sherlock” and “War Horse” in 2011

“Masterpiece” roots: “To the Ends of the Earth” in 2006 and “The Last Enemy” in 2008

Cumby was brilliant as an arrogant Brit gaining self-knowledge on a nauseating sea journey in 1812 in “To the Ends of the Earth.” His future success was easy to deduce. In a perfect casting trick, he is about to star as Julian Assange in “The Man Who Sold the World.”

Romola Garai

Known for: “Atonement” in 2007 and “The Hour”

“Masterpiece” roots: “Daniel Deronda” in 2003 and “Emma” in 2010

If there’s going to be a Next Kate Winslet, it should be Garai. She’s a powerful lead in “The Hour,” and her turn as Jane Austen’s Emma Woodhouse was one of the best among many. She can bring full-on drama and wry comedy equally well.

Hugh Bonneville

Known for: “Downton Abbey”

“Masterpiece” roots: “Madame Bovary” in 2000, “The Cazalets” in 2001, “Daniel Deronda” and “Dr. Zhivago” in 2003

Turns out the doughy Lord Grantham has been the noble lurking in countless PBS-BBC costume dramas. Bonneville was equally memorable as the simple man ruined by Madame Bovary and as the sadistic Lord Grandcourt in “Deronda.”

Carey Mulligan

Known for: “An Education” in 2009 and “Shame” and “Drive” in 2011

“Masterpiece” roots: “Bleak House” in 2006, “The Amazing Mrs. Pritchard” in 2007, “Northanger Abbey” and “My Boy Jack” in 2008

The Oscar nominee, who is married to Marcus Mumford and about to star as Daisy Buchanan in Baz Luhrmann’s upcoming “Great Gatsby,” can wear a corset like nobody’s business. Coincidentally, “Downton” creator Julian Fellowes helped her get her start.

James Frain

Known for: “24,” “True Blood,” “Grimm,” “Invasion,” and “The Tudors”

“Masterpiece” roots: “The Buccaneers” in 1995, and “The Mill on the Floss” in 1997

This utility player is all over American TV these days, with guest spots on everything from “Law & Order: SVU” to “Burn Notice.” But his early years were distinguished by a number of veddy British productions.

Keira Knightley

Known for: “Pride & Prejudice” in 2005 and “Atonement” in 2007

“Masterpiece” roots: “Oliver Twist” in 1999 and “Dr. Zhivago” in 2003

She broke through in Austen, and got an Oscar nomination, but we knew her when she did Dickens and Pasternak. Knightley stood out from the get-go as an actress who’d make her mark.

Matthew Macfadyen

Known for: “Pride & Prejudice” in 2005

“Masterpiece” roots: “The Way We Live Now” in 2001.

He was the emo Mr. Darcy opposite Keira Knightley; this month he’ll star in a new BBC America series called “Ripper Street.” But back in the day, he was featured in PBS’ excellent Trollope miniseries “The Way We Live Now.” His recent “Masterpiece” performances in “Little Dorritt” and “Any Human Heart” have been top-notch.

Hugh Dancy

Known for: “Ella Enchanted” in 2004 and “Martha Marcy May Marlene” in 2011

“Masterpiece” roots: “Madame Bovary” in 2000, “Daniel Deronda” in 2003

He’s married to Claire Danes, whom he met on the set of “Evening” in 2006. But we met him back in the day, when he was one of the “Masterpiece” go-to leads.

Ruth Wilson

Known for: “Luther”

“Masterpiece” roots: “Jane Eyre” in 2007

She’s one of TV’s most chilling killers on “Luther,” as the brilliant Alice. But we still remember seeing her blushing in the dark corners of Thornfield Hall in a solid adaptation of Charlotte Bronte’s classic.

Damian Lewis

Known for: “Homeland”

“Masterpiece” roots: “The Forsyte Saga” in 2002

OK, OK, he was in “Band of Brothers” first. But he was part of the ensemble. In the excellent “Forsyte Saga,” he masterfully drove the drama as the shy, pathetic Soames, clinging to old-fashioned values.Continued...