As Apple and Samsung escalated a multibillion-dollar war over one of the hottest consumer gadgets of our time, the tablet computer, a little-known judge did for Apple what the company couldn’t do on its own: She shut down the competition.

The stunning move by U.S. District Judge Lucy H. Koh to temporarily order Samsung’s tablets off the shelves last month rippled across the tech industry because her decision came as sales of the devices are surging. Samsung’s Galaxy Tab was one of the few 10-inch screen tablets that could go toe-to-toe with Apple’s iPad.

“If she wasn’t known before, she is now,” said Florian Mueller, an intellectual-property analyst who runs the patent blog FOSS Patents. “Her decisions on these cases will be cited a lot going forward.”

For Koh, the reason for the sales ban was clear.

“Although Samsung has a right to compete, it does not have a right to compete unfairly, by flooding the market with infringing products,” Koh wrote in her opinion last month. She said Apple would be “irreparably harmed” if sales of the Galaxy Tab continued.

Judge Lucy Koh (John Stubler)

Now, as the case heads to a jury trial this month, all eyes are on the 43-year-old judge. Apple, with 63 percent of the market, and Samsung, with a nearly 9 percent share, rank one and two among tablet makers.

On the one hand, Koh is the ideal person to review such suits. She is an expert on intellectual-property law, having practiced patent litigation for about a decade in private practice. In 2006, as a lawyer at McDermott Will & Emery, she represented Creative Technology in a federal suit accusing Apple of infringing patents with its iPod music player. Apple countersued but ended up paying Creative $100 million for licensing fees.

On the other hand, she is a rookie judge who was appointed by President Obama in 2010. In just one year, she has taken on hundreds of cases, and she now grapples with the massive attention the tablet and smartphone patent suits have drawn from the captains of the high-tech industry.

It’s a baptism by fire, said Judge Ronald M. Whyte, a noted expert on patent law and Koh’s mentor on the District Court in San Jose. He said it is typical to see Koh working extremely long hours, cutting her vacations short for work and coming in to study cases on weekends.

“She isn’t afraid to take things head-on,” Whyte said. “She takes things very seriously.”

The case before Koh is one in an array of lawsuits playing out in courtrooms around the world as tablet and smartphone makers use patents not only to protect their ideas but also to weaken their rivals.

Apple’s push in the courts partly stems from Steve Jobs, the late chief executive of Apple, who said he was willing to declare “thermonuclear war” on his rivals to protect the iPhone and iPad, according to a biography written by Walter Isaacson.

In April 2011, Apple sued Samsung in the U.S. District Court of the Northern District of California for allegedly copying Apple’s products, even though Samsung was a major supplier of screens for those gadgets.

In December, Koh rejected Apple’s request for a preliminary injunction on those devices. But an appeals court agreed in part with Apple’s claims and sent the request back to Koh to reconsider.

On June 26, Koh ordered a temporary freeze on Galaxy Tab 10.1 sales.

To prove her point, Koh, in a dramatic display, held up the iPad and Galaxy Tab above her head and asked Samsung’s counsel to distinguish the gadgets. The lawyers struggled to get it right.

“Apple’s interest in enforcing its patent rights is particularly strong because it has presented a strong case on the merits,” Koh wrote.

Days later, she added another injunction on Galaxy Nexus smartphones, though a federal appeals court in early July lifted that sales ban.

Samsung called the decision “unfortunate” and vowed to fight back in courts. Samsung and Apple declined to comment for this story.

Some legal experts say Koh does not necessarily favor Apple. She has also demanded top company executives work out their differences in a settlement, which she believes is preferable to court decisions that can wind their way through the appeals process, observers of the case say. Apple chief executive Tim Cook has begun meeting with Samsung executives, according to people familiar with the matter who spoke on condition of anonymity because the talks are private.

“Judge Koh might reasonably bear the brunt of public criticism, but . . . this is really a bigger indictment of the patent system,” said Mark Lemley, a professor at Stanford Law School.

Lemley estimates smartphone companies have doled out $600 million to $700 million in legal fees over patent disputes. They have spent between $15 billlion and $20 billion on massive patent acquisitions that allow the richest firms to leapfrog competitors by buying up inventions.

Silicon Valley firms have become too eager to sue for their business interests, U.S. Appeals Court Judge Richard Posner has said. In June, he threw out Apple’s suit against Motorola on smartphone patents. He rejected Apple’s request for an injunction on Motorola smartphone sales, calling the infringements “minor-seeming” and claims of harm “implausible.”

Koh declined to comment for this story. Those who know her said she prefers staying out of the spotlight, despite the high-profile nature of the case before her.

At Harvard Law School, the hardworking student preferred to quietly soak up lessons from the back seats of class.

“Way back,” she said with emphasis in a 2007 interview.