Doll & Co. was founded in Nüremburg, Germany in 1898 by John Sondheim and tinsmith Peter Doll. The company had a variety of both steam engines and steam toys, and were widely distributed throughout Europe, the UK and the United States. Doll made and sold model steam engines as well as other steam toys and accessories such as tractors, saw mills, fountains and a Ferris Wheel. The company were large exporters, sending most of their wares to England and the United States.
Max Bein, Sondheim's nephew, joined the company just before the outbreak of the WW1 as a third partner. After WW1, the manufacturing of model steam engines continued in the 1920s and 1930s together with that of trains, a steam car and a lorry.
Doll was bought up by Fleischmann around 1935 due to the Aryanization laws -the original founders were Jewish- and at first carried on under its old name (strangely enough, the Fleischmann family was also of Jewish origins, but managed to obtain an 'Aryan' certificate, whereas Doll did not).
Max Bein and his family managed to escape Germany and the horrors of the Holocaust, winding up in the United States, and settling in the Boston area. After the war, Fleischmann offered to return the company back to the original owners, but they declined, accepting a buyout of their shares instead.
For a more in-depth story about the Bein family and what happend when they fled to the States, read this article on jewmag.com
See also Fleischmann steam models
What's it worth? Take a look at this Doll Steam price guide: sold listings for a value indication.