There is probably no other major city in America whose original name is as disputed as that of Los Angeles. We do know that current name Los Angeles is Spanish for The Angels. The official name, City of Los Angeles has been the city’s official name since at least it became an American city in 1850.
On Wednesday, August 2, 1769, Father Juan Crespi, a Franciscan priest accompanying the first European land expedition through California, led by Captain Fernando Rivera Y Moncado, described in his journal a "beautiful river from the northwest" located at "34 degrees 10 minutes." They named the river Nuestra Señora de los Angeles de la Porciúncula. In the Franciscan calendar, August 2 was the day of the celebration of the feast of the Perdono at the tiny Assisi chapel of Saint Francis of Assisi. Early in Saint Francis’ life, the Benedictines had given him this tiny chapel for his use near Assisi. The chapel, ruined and in need of repair, was located on what the Italians called a porziuncola or "very small parcel of land." Painted on the wall behind the altar was a fresco of the Virgin Mary surrounded by angels. Now contained within a Basilica, the chapel was named Saint Mary of the Angels at the Little Portion. The newly discovered "beautiful river" that Father Crespi wrote of in 1769 (later named the Los Angeles River) was named in honor of this celebration and this chapel.
In 1781, a new settlement was established along that river. What this settlement was originally named is where historians disagree.
Also see: What might have the founders of Los Angeles looked like?
In his book "The Founding Documents of Los Angeles, A Bilingual Edition," Los Angeles historian Doyce B. Nunis Jr., gives the town’s original name as El Pueblo de la Reyna de los Angeles (English: The town of the Queen of Angels). Nunis points to evidence in the earliest handwritten map of the new settlement (held at Bancroft Library, UC Berkeley), dated just four years after the town’s founding in 1781, that shows the town name as El Pueblo de la Reyna de los Angeles (Reyna may also be spelled Reina, English: Queen).
On the other hand, Monsignor Francis J. Weber, history writer and archivist for the Los Angeles Archdiocese, argues that the town’s original name was El Pueblo de Nuestra Señora de los Angeles de Porciúncula (English: The town of Our Lady of the Angels of Porciúncula). He stated that this name was derived from the name Father Crespi gave to the adjacent river in 1769. The words Reyna or Reina were only added later and the name in the 1785 map was simply a continuation of that mistake.
Other possibilities that have been offered:
Also see Pronouncing "Los Angeles"
and Nicknames for Los Angeles