Mallard was one of 35 near-identical A4-class locomotives designed by renowned engineer Sir Nigel Gresley - the man behind the Flying Scotsman.
The six survivors include Dominion of Canada, which now sits next to Mallard at the National Railway Museum after it was shipped from Montreal last October and restored especially for the anniversary.
The Dwight D Eisenhower - another transatlantic expat - has also rolled back into York from America and been treated to a scrub-up for the occasion. Union of South Africa, the Sir Nigel Gresley and the Bittern have joined them around the museum's Great Hall turntable for The Great Gathering.
Bittern travelled from London Kings Cross under its own steam on Saturday after it was granted special permission to make a celebratory 90mph run up the East Coast Main Line to York - 15mph over the normal limit for steam trains. It reached a top speed of 92mph and arrived on time.
For no more than a couple of minutes on July 3rd, 1938, Mallard thundered along at speeds that have remained unmatched by any steam locomotive for three-quarters of a century. A handful of men in soot-stained overalls had pushed the roaring engine to 126mph, marking the pinnacle of steam power.
Despite its unique place in history, Mallard was one of 35 near-identical A4-class locomotives designed by renowned engineer Sir Nigel Gresley - the man behind the Flying Scotsman. Organisers say the anniversary celebration is a "a once-in-a-lifetime" event.
What we're planning is a major celebration - people will be coming from four corners of the earth. The gathering of the six locomotives is the jewel in the crown really. Mallard didn't really set out on that run to be a record-breaker, They went to see what they could get out of it and it had a test car on the back which was noting down all the measurements."And they got the chance really on Stoke Bank. And they went for it. They knew that the only chance they could get to go that fast was on this part of the line.
The record was made over not more than a couple of miles. It was quite a short distance but it was enough to get Mallard's place in the record books.
– Anthony Coulls, senior curator of rail vehicle collections
Dozens of journalists have turned up at the NRM to witness the historic event. They and pilgrims from all over the world including Canada, the US and Australia have gathered to celebrate Mallard's achievement and witness a sight never seen before, which fulfills the dreams of rail fans everywhere.