The LNER A4 Mallard is a record-breaking train. It is the fastest steam train in the world reaching 126mph (203 km/h) on 3rd July 1938. It was designed by Sir Nigel Gresley, the same person who designed the Flying Scotsman, and it was made in Doncaster rail works. It is currently on display at the National Railway Museum in York. Here's a photo
There are entire threads about it. DTG’s official stance is that they’re not actively developing steam anymore but welcome 3rd parties that would like to work on it. That said, I think we should keep the steam suggestions coming, either to show DTG that steam shouldn’t be abandoned or for 3rd parties if any actually come through.
DTG's discontinuation of steam content aside, I think 60007 Sir Nigel Gresley would be more appropriate for a railtour DLC, or perhaps Bittern once it goes through overhaul