The History of Santa Claus & Father Christmas — just a bit of seasonal fun :) http://www.arthuriana.co.uk/xmas/index.htm 

St Nicholas of Myra—an assessment of the early stories of his life & their historicity: http://www.livius.org/articles/person/nicholas-of-myra/ & see also https://www.roger-pearse.com/weblog/2015/02/03/the-literary-development-of-the-life-of-st-nicholas-of-myra-santa-claus/

The English Father Christmas — merged with St Nicholas/Santa Claus in the late 19th century, but originally separate & gave no gifts to children! http://www.arthuriana.co.uk/xmas/pages/english.htm

'I Am Here, Sir Christëmas', a 15th-century carol with a very early personified Christmas: http://www.hymnsandcarolsofchristmas.com/Hymns_and_Carols/i_am_here_sir_christemas.htm

'The Examination and Tryal of Old Father Christmas' (1686): https://luna.folger.edu/ll/thumbnailView.html?startUrl=%2F%2Fluna.folger.edu%2Fluna%2Fservlet%2Fas%2Fsearch%3Fos%3D0%26mid%3DFOLGERCM1~6~6~204874~112692%26bs%3D10 & http://www.hymnsandcarolsofchristmas.com/Poetry/examination__and__tryal_of.htm

Dickens's Ghost of Christmas Present, by John Leech, 1843, a version of Father Christmas & dressed in green: https://commons.m.wikimedia.org/wiki/File:Scrooges_third_visitor-John_Leech,1843.jpg

Old Christmas on the cover of the 1842 Christmas supplement to the London Illustrated News: http://www.iln.org.uk/iln_years/year/xmas2.htm

Jolly Old Christmas from the Christmas issue of the Illustrated London News, 1844: http://www.iln.org.uk/iln_years/year/xmas2.htm

A Victorian-era German 'Father Christmas' with a foliage beard.

Turning to look at St Nicholas/Santa Claus, an article on Stephen Nissenbaum's research into the early 19th-century American creation of Santa Claus & the sanitisation of Christmas: https://www.threemonkeysonline.com/christmas-reborn-the-creation-of-a-consumer-christmas-professor-steven-nissenbaum-in-interview/

A very early illustration of 'Sante Claus' from The Children's Friend, William B. Gilley, 1821: https://www.stnicholascenter.org/pages/origin-of-santa/

Robert Weir's painting of St Nicholas, c. 1837: https://americanart.si.edu/artwork/st-nicholas-27465 For more on this painting and the Knickerbocker interest in reinventing St Nicholas/Santa Claus, see https://www.jstor.org/stable/3050448?seq=1#page_scan_tab_contents

St Nicholas/Santa Claus before Thomas Nast—illustrations to Moore's 'Night Before Christmas' by Louis Prang, 1864: https://www.americanantiquarian.org/Exhibitions/Christmas/prang.htm

Thomas Nast's illustrations for Clement Clarke Moore's 'A Visit from Saint Nicholas', 1869: https://www.americanantiquarian.org/Exhibitions/Christmas/nast.htm

Thomas Nast's Santa Claus and his Works, c.1869: https://www.stnicholascenter.org/pages/origin-of-santa/

The American Santa Claus as a Christmas gift-giver was first noted in England in 1879—19th-century folklorists initially puzzled by him, not knowing who he was, with one guessing it was ‘Santa Cruz, the Holy Cross’ which brought the presents: http://www.arthuriana.co.uk/xmas/pages/history.htm

By the late 19th/early 20th century, the English Father Christmas and the American Santa Claus had become interchangeable & largely indistinguishable... https://twitter.com/caitlinrgreen/status/1341511493196636161?s=19

Old Father Christmas riding on a Yule goat, 1836, & Father Christmas as gift-giver on an English postcard of 1919: https://commons.m.wikimedia.org/wiki/File:Old_Christmas_riding_a_goat,_by_Robert_Seymour,_1836.jpg & https://en.m.wikipedia.org/wiki/File:Father_Christmas,_Tuck_Photo_Oilette_postcard_1919,_front.jpg

By the early twentieth century, the American Santa Claus had also spread to Japan, as seen in this image of a modern-looking Santa Claus from 1914: https://commons.m.wikimedia.org/wiki/File:1914_Santa_Claus.jpg

Worth noting, incidentally, that the modern-looking Japanese Santa dates from well before the first Coca-Cola Santa ad campaign in 1931; see further https://www.snopes.com/fact-check/the-claus-that-refreshes/ on the myth of Coca-Cola's creation of the modern Santa :)

A couple more pre-Coca-Cola Santas, from 1918 and 1902.

Before he started endorsing Coca-Cola, a very modern-looking Santa Claus had previously endorsed White Rock mineral water and ginger ale… (images from Life magazine, Dec 1923 and Dec 1924): http://www.whiterocking.org/santa.html 

Santa endorsed products well before White Rock and Coca-Cola too — here's the label from a box of Santa Claus Sugar Plums, 1868: https://commons.m.wikimedia.org/wiki/File:Santa_Claus_Sugar_Plums,_1868.png

The first of J.R.R. Tolkien's letters from Father Christmas, 1920—although he used the English name for the Christmas visitor, he also made liberal use of elements from the American Santa Claus lore and included both elves & goblins: https://theconversation.com/amp/j-r-r-tolkiens-christmas-letters-to-his-children-bring-echoes-of-middle-earth-to-the-north-pole-89464

'Twas the night before Christmas, when all thro' the house
Not a creature was stirring, not even a mouse;
The stockings were hung by the chimney with care,
In hopes that St. Nicholas soon would be there…
(pic= http://www.americanantiquarian.org/Exhibitions/Christmas/mcloughlinedition.htm, 1896)

Some additional watercolors used in the 1896 edition of A Visit from Saint Nicholas, published by McLoughlin Brothers :) https://www.americanantiquarian.org/Exhibitions/Christmas/mcloughlinedition.htm