Santa and Father Christmas have disparate origins, but as of the 21st century have essentially coalesced into one figure; in fact, many younger Brits now refer to "Santa" instead of Father Christmas—the use of the term Father Christmas is now almost seen as a more "formal" or "traditional" way of saying Santa in Britain.

The name "Santa Claus" is actually an Anglicization (altering a non-English word to sound more English-like) of the Dutch term "Sinterklaas", which meant Saint Nicholas. So "Santa Claus" was basically an evolved way of saying Saint Nicholas. Interestingly, Saint Nicholas-derived figures originally gave their gifts on St. Nicholas Day (Dec. 6), but over time as the legend of St. Nicholas coalesced with other legends such as that of Christkindl—a Protestant-created personification of the Christ-Child (the origin to the Santa alt-name "Kris Kringle") that instead delivered the gifts on Dec. 25 , Santa's gift-giving day moved to December 25.

While the legend of Saint Nicholas himself is said to be the origin of Santa's giving of gifts to children, other Santa traditions have evolved from a variety of sources, particularly in regard to the Wild Hunt of Odin, a pagan god who himself rather resembled the modern image of Father Christmas/Santa Claus in depictions. Odin's Wild Hunt is thought to have influenced the myth of "Santa's reindeer", as it involved a ghostly procession flying through the sky. None of these Santa-associated themes really became cemented until certain authors in the 19th century created landmark works, such as "A Visit from St. Nicholas" (widely known as "Twas the Night Before Christmas"), which itself was the source of many common Santa tropes.

In terms of the ubiquity of Santa... this can be said to have come rather quickly after the introduction of memes like "A Visit from St. Nicholas" in the 19th century, as well as the first depictions of Santa in media which occurred shortly thereafter. The myth had already been going on for centuries, but it finally attained a solid base around that time, and spread to cultures around the world through (primarily American) media influence over the next two centuries. The commercialization of Christmas occurred nearly simultaneously with the emergence of Santa as a pop culture icon, so whether one was influenced by the other remains debatable. American corporations marketed Christmas as a gift-giving holiday, and often used imagery of Santa, and the rest is history.

As for Father Christmas, he remained a relatively separate figure that simply personified Christmas rather than being an obese man who gave gifts to children... until after the 19th century, when media such as "A Visit from St. Nicholas" slowly set in motion the merging of Father Christmas with Santa.