David Cameron becomes UK's youngest PM

David Cameron, responsible for modernizing the party of right-wing icon Margaret Thatcher, became Britain's youngest Prime Minister in almost 200 years on Tuesday.

Following tradition, Queen Elizabeth II appointed Cameron at Buckingham Palace.

Cameron and Clegg agreed to form a coalition after Cameron's Conservative Party won the most seats in Britain's May 6 national election, but fell short of winning a majority of seats in Parliament. Liberal Democrat leader Nick Clegg would become deputy Prime Minister.

The coalition has already agreed on a five-year, fixed-term Parliament -- the first time Britain has had the date of its next election decided in advance.

As Prime Minister in charge of Britain's first coalition government in 65 years, Cameron will have to contend not only with the tensions within his own party, but also with the dueling demands of his Liberal Democratic partners. (AP Image)

David Cameron's election as the Prime Minister of the United Kingdom came after Gordon Brown stepped down from his post, enabling the former to cap a gripping election saga that returns the Tories to government after 13 years of Labour Party rule. (AP Image)

Following tradition, Queen Elizabeth II appointed Cameron as the Prime Minister at Buckingham Palace , after an election that left no party with a majority. (AP Image)

Within minutes, the 43-year-old Cameron was installed at No. 10 Downing Street, becoming the youngest Prime Minister in almost 200 years, since Lord Liverpool took office at age 42. (AP Image)

The smooth, self-assured Cameron moved swiftly to weed out the old guard, replacing the party's mean-spirited image with a kinder, more socially progressive philosophy that he called compassionate Conservatism.

In this picture, David Cameron and his wife Samantha meet Cabinet Secretary Gus O'Donnell in the Cabinet Room of 10 Downing Street. (AP Image)

Arriving at London's Downing Street hand-in-hand with his wife, Samantha, Cameron said he believed that Britain's "best days lie ahead." (AP Image)

Britain's new government could spell changing relationships with its foreign allies.

President Barack Obama telephoned to congratulate Cameron, and invited him to visit Washington this summer, according to the White House. (AP Image)

After days of hard bargaining with his former political rivals, Liberal Democrat leader Nick Clegg became the deputy Prime Minister, the post hailed as a rare and prestigious one . Four other Liberal Democrats also received Cabinet posts. (AP Image)

Cameron and Clegg agreed to form a coalition after Cameron's Conservative Party won the most seats in Britain's May 6 national election, but fell short of winning a majority of seats in Parliament.

This would be Britain's first full coalition government since World War II. (AP Image)

As Prime Minister in charge of Britain's first coalition government in 65 years, Cameron will have to contend not only with the tensions within his own party, but also with the dueling demands of his Liberal Democratic partners.

The priority will be to spur a once high-flying economy, rooted in world-leading financial services, that has run into hard times. (AP Image)