Year 1940 (MCMXL) was a leap year starting on Monday (link will display the full calendar) of the Gregorian calendar.

Below, the events of World War II have the "WWII" prefix.

Stefani Joanne Angelina Germanotta (/ˈstɛfəniː dʒʌrməˈnɑːtə/ STE-fə-nee jurr-mə-NAH-tə; born March 28, 1986), known by her stage name Lady Gaga, is an American singer and songwriter. Born and raised in New York City, she primarily studied at the Convent of the Sacred Heart and briefly attended New York University's Tisch School of the Arts before withdrawing to focus on her musical career. She began performing in the rock music scene of Manhattan's Lower East Side, and was signed with Streamline Records by the end of 2007. During her employment as a songwriter for the record company, her vocal abilities captured the attention of recording artist Akon, who signed her to his label Kon Live Distribution.

Lady Gaga came to prominence as a recording artist following the release of her debut album The Fame (2008), which was a critical and commercial success that topped charts around the world and included the international number-one singles "Just Dance" and "Poker Face". After embarking on the The Fame Ball Tour, she followed the album with The Fame Monster (2009), which spawned the worldwide hit singles "Bad Romance", "Telephone" and "Alejandro". The album's success allowed her to embark on the eighteen-month long Monster Ball Tour, which later became one of the highest-grossing concert tours of all time. Her most recent album Born This Way (2011) topped the charts of most major markets and generated more international chart-topping singles, including "Born This Way", "Judas" and "The Edge of Glory". Besides her musical career, she involves herself with humanitarian causes and LGBT activism.

Joan Crawford (March 23, 1905 – May 10, 1977), born Lucille Fay LeSueur, was an American actress in film, television and theatre.

Starting as a dancer in traveling theatrical companies before debuting on Broadway, Crawford was signed to a motion picture contract by Metro-Goldwyn-Mayer in 1925. Initially frustrated by the size and quality of her parts, Crawford began a campaign of self-publicity and became nationally known as a flapper by the end of the 1920s. In the 1930s, Crawford's fame rivaled MGM colleagues Norma Shearer and Greta Garbo. Crawford often played hardworking young women who find romance and financial success. These "rags-to-riches" stories were well received by Depression-era audiences and were popular with women. Crawford became one of Hollywood's most prominent movie stars and one of the highest paid women in the United States, but her films began losing money and by the end of the 1930s she was labeled "box office poison".

After an absence of nearly two years from the screen, Crawford staged a comeback by starring in Mildred Pierce (1945), for which she won the Academy Award for Best Actress. In 1955, she became involved with the Pepsi-Cola Company through her marriage to company Chairman Alfred Steele. After his death in 1959, Crawford was elected to fill his vacancy on the board of directors but was forcibly retired in 1973. She continued acting in film and television regularly through the 1960s, when her performances became fewer; after the release of the British horror film Trog in 1970, Crawford retired from the screen. Following a public appearance in 1974, after which unflattering photographs were published, Crawford withdrew from public life and became more and more reclusive until her death in 1977.

Justin Drew Bieber ( /ˈbiːbər/ BEE-bər, born March 1, 1994) is a Canadian Pop/R&B singer-songwriter, musician, and actor. Bieber was discovered in 2008 by Scooter Braun, who came across Bieber's videos on YouTube and later became his manager. Braun arranged for him to meet with Usher in Atlanta, Georgia, and Bieber was soon signed to Raymond Braun Media Group (RBMG), a joint venture between Braun and Usher, and then to a recording contract with Island Records offered by L.A. Reid. Bieber's debut single, "One Time", was released in 2009 and peaked in the top twenty in Canada and charted in the top thirty in several international markets. His debut album, the seven-track EP My World, followed in November 2009, and was soon certified platinum in the United States. He became the first artist to have seven songs from a debut album chart on the Billboard Hot 100.

Onika Tanya Maraj (born December 8, 1982), known by her stage name Nicki Minaj ( /mɪˈnɑːʒ/), is a Trinidadian-born American rapper and singer-songwriter. She was born in Saint James, Trinidad and Tobago and when she was 5 years of age she moved to the New York City borough of Queens, where she grew up.

After releasing three mixtapes between 2007 and 2009 and being signed to Young Money Entertainment in August 2009, Minaj released her debut album, Pink Friday, in November 2010. It quickly became a commercial success, peaking at number one on the U.S. Billboard 200 and being certified Platinum by the Recording Industry Association of America (RIAA) a month after its release. She became the first female solo artist to have seven singles on the Billboard Hot 100 at the same time. Her second single, "Your Love", reached number 1 on the Billboard Hot Rap Songs chart, making Minaj the first female artist to top the chart unaccompanied since 2002. She also became the first female artist to be included on MTV's Annual Hottest MC List. Minaj was named the 2011 Rising Star by Billboard. Her second studio album, Pink Friday: Roman Reloaded was released on April 3, 2012.