Donald Trump on Friday became the 45th president of a bitterly divided country following a long, bruising election cycle, pledging that "Jan. 20, 2017, will be remembered as the day the people became the rulers of this nation again."

He said that an elite few has controlled the country for too long. Trump asserted that he would be "transferring power from Washington, D.C., and giving it back to you, the people."

Trump vowed to be a president for all people and said that "together we will determine the course of America and the world for many, many years to come." He stressed an "America first" policy on issues ranging from trade to immigration to foreign affairs.

"America will start winning again, winning like never before," he said. "We will bring back our jobs, we will bring back our borders, we will bring back our wealth and we will bring back our dreams."

In a wide-ranging but short speech, Trump promised to "buy American and hire American," unite the world against "radical Islam" and rebuild the nation's highways, railways and airports.

He told the crowd, "Whether we are black or brown or white, we all bleed the same red blood of patriots."

The 45th president praised his predecessor, President Barack Obama, as well as first lady Michelle Obama. "They have been magnificent," he said.

The Obamas weren't the only former first family in attendance. Jimmy and Rosalynn Carter, George W. and Laura Bush, and Bill and Hillary Clinton all attended the ceremony.

Clinton, who lost the presidential election to Trump in a stunning and unexpected upset, explained her decision to attend the inauguration on Twitter.

"I'm here today to honor our democracy & its enduring values. I will never stop believing in our country & its future," she tweeted.

George H.W. and his wife Barbara were notably absent from the ceremony, as both remain hospitalized. The 41st president is in the ICU with a respiratory problem, and the former first lady was hospitalized with bronchitis as a precaution, the family's spokesman said.

In a letter to Trump, dated Jan. 10, Bush wrote, "My doctor says if I sit outside in January, it likely will put me six feet under. Same for Barbara. So I guess we're stuck in Texas."

Chief Justice John Roberts presided over Trump's swearing-in. The president used two bibles -- one given to him by his mother during his childhood and another that Abraham Lincoln used when he was first sworn in as president. Associate Supreme Court Justice Clarence Thomas officiated the swearing-in for Vice President Mike Pence.

Robert Burck, a Times Square street performer better known as The Naked Cowboy, made the trip to D.C. for the inauguration, strutting through the crowd in his signature cowboy hat, boots and briefs with "Trump" written on his rear.

He wore nothing else despite the chill and the drizzle. The Naked Cowboy posed for photos and strummed a song on his guitar, supportive of Trump's taking on of corporations.

Joseph Manzo, the assistant principal of Staten Island Technical High School, brought 41 students via bus to the inaugural ceremonies. They posed for a group photo on the National Mall.

Manzo said he was proud to watch the peaceful transfer of power, but called Trump's speech "pessimistic."

A Staten Island Tech junior, Sophia Corst, 16, of Bay Ridge, Brooklyn, who wore a red "Make America Great Again" cap, said being near the U.S. Capitol for the inauguration "takes our patriotism to a whole new level."

On the National Mall Friday morning, Anthony Messina, 33, of Brooklyn said he's excited about the inauguration because Donald Trump will bring "real hope and change."

Thousands of anti-Trump protesters were expected among an inauguration crowd that organizers estimated would be upward of 900,000. Many demonstrators will participate in the "Women's March on Washington" on Saturday. Protests are also planned in other cities in the United States and abroad, including in New York.

Trump, 70, enters the White House with work to do to bolster his image. During a testy transition period since his stunning November election win, the wealthy New York businessman and former reality TV star has repeatedly engaged in Twitter attacks against his critics, so much so that one fellow Republican, Sen. John McCain, told CNN that Trump seemed to want to "engage with every windmill that he can find."

An ABC News/Washington Post poll this week found only 40 percent of Americans viewed Trump favorably, the lowest rating for an incoming president since Democrat Jimmy Carter in 1977, and the same percentage approved of how he has handled the transition. 

His ascension to the White House, while welcomed by Republicans tired of Obama's eight years, raises a host of questions for the United States.

Trump campaigned on a pledge to take the country on a more isolationist, protectionist path and has vowed to impose a 35 percent tariff on goods on imports from U.S. companies manufacturing abroad.

His desire for warmer ties with Russian President Vladimir Putin and threats to cut funding for North Atlantic Treaty Organization nations has allies from Britain to the Baltics worried that the traditional U.S. security umbrella will be diminished.

In the Middle East, Trump has said he wants to move the U.S. embassy in Israel from Tel Aviv to Jerusalem, at the risk of angering Arabs. He has yet to sketch out how he plans to carry out a campaign pledge to "knock the hell out of" Islamic State militants.

More than 50 Democratic lawmakers stayed away from the proceedings to protest Trump, spurred on after he derided Rep. John Lewis of Georgia, a hero of the civil rights movement, for calling him an illegitimate president.

- With Emily Ngo and Edward B. Colby