By Lisa Richwine

LOS ANGELES (Reuters) - A judge called Sumner Redstone's deposition "strong evidence" that the media mogul knew what he was doing when he ejected an ex-girlfriend from his life, suggesting Redstone has the upper hand in a trial over his mental competence that began on Friday.

Although the 92-year-old billionaire, who has majority control of media companies Viacom and CBS, had some trouble speaking in the deposition and did not respond coherently to certain questions, he was clear on the central issue.

Redstone repeatedly called the ex-girlfriend, Manuela Herzer, a "fucking bitch" in the deposition circulated in the packed courtroom, and accused her of stealing money from him. When asked what he wanted at the end of the trial, Redstone replied: "I want Manuela out of my life. Yeah."

Herzer is suing Redstone over her removal in October as the billionaire's designated health care, arguing that Redstone was not mentally competent at the time he made the decision. Redstone's lawyers say he has difficulty speaking but is mentally fit.

Los Angeles Superior Court Judge David Cowan reviewed Redstone's video deposition privately, and appeared to sympathize with the ailing Redstone.

"He has told me now, best he can, what he wants," said Cowan, who will decide the case without a jury. "That's strong evidence."

"Your burden now is a hard one," Cowan said to Herzer's attorneys, who must prove that Redstonewas mentally incompetent when he removed Herzer from his plans.

Pierce O'Donnell, who represents Herzer, responded that Redstone's answers to his own lawyer's questions in the deposition were programmed and rehearsed.

Redstone's attorneys asked Cowan to dismiss the lawsuit and the judge requested both sides submit legal briefs over the weekend, saying he could rule on Monday.

Referring to Redstone, Cowan said: "How can I sit here and say, after listening to that video, no you can't have what you want?"

Speaking to reporters outside court, ODonnell said he was confident Herzer could defeat the motion to dismiss.

"The question isnt whether [Redstone] made that decision, but why did he make that decision?"

Herzer, wearing a black suit at the first day of the trial held in a windowless courtroom on the sixth floor of a downtown Los Angeles courthouse, showed little emotion throughout the day but shook her head and nodded at various points in the testimony. Redstone's daughter Shari and her son Brandon Korff also attended.

The trial, set to run through May 16, is being closely watched by shareholders of Viacom Inc and CBS Corp. Redstone stepped down as executive chairman of both companies earlier this year, assuaging some investor questions about his influence at the company.

But some concerns remain about what will happen, and when, to his roughly 80 percent of the voting shares in both companies, held through his National Amusements movie theater company.

If Herzer, 52, proves her case, the outcome could cause a chain of events that would result in the transfer of Redstones controlling stake in both companies to a seven-person trust which includes Viacom CEO Philippe Dauman and Redstone's daughter Shari, which could alter the course of both companies.

If she loses the case, control remains in Redstone's hands. The transfer of his shares to the trust is also scheduled to take place upon his death.

TOUGH CASE TO MAKE

In order to win, Herzer must show that Redstone had sufficient mental capacity when he named Herzer his health care agent in September 2015, but was incompetent the following month when he removed her.

In the days and weeks before she was ejected, Herzer made hundreds of thousands of dollars of purchases on Redstones credit card and "executed a $5 million grant agreement with Mr.Redstone for the benefit of her foundation," according to a Redstone court filing.

That suggests Herzer thought Redstone was mentally competent to approve the expenditures,Redstone's attorneys argue.

Herzer's lawyers argue that Redstone's health deteriorated sharply after the end of a relationship with another girlfriend.

Redstone had a harder time with O'Donnell's queries, according to the deposition transcript.Redstone did not answer when asked what his name was before he changed it to SumnerRedstone, and seemed unable to answer questions about when Herzer lived with him.

However, when asked by his lawyer who should make his health care decisions if he no longer could, Redstone clearly named his daughter, Shari, who is a board member at Viacom and CBS.

A geriatric psychiatrist hired by Herzer, Stephen Read, testified on Friday that Redstone has "uncontrollable outbursts of anger" which interfere with his ability to reason.

At an in-person examination earlier this year, Read asked Redstone to identify colored shapes.

"He did very poorly," Read said. Asked to point to a blue star, Redstone pointed at a green square, the psychiatrist said.

According to Read, people close to Redstone arrange for him to bet on sports and always win. The games are prerecorded, and Redstone is persuaded to bet on the winning team. Redstoneappears to have no idea that the games he is watching are not live and does not realize that his winning is staged, Read said.

On cross examination, Read acknowledged that it would now be "very difficult" for Herzer to take part in Redstone's health decisions, given his feelings about her.

(Additional reporting by Sue Horton in Los Angeles and Jessica Toonkel in New York; Writing by Dan Levine; Editing by Nick Zieminski and Andrew Hay)