it was a fairly small German knifemaker who was known for exceptional quality. They at one point were regarded much more highly than Henckels and Wustof. where these two companies jumped on the mass production market after World War 2 Gustav did not. They believed in quality over quantity and that in the end killed them. They couldn't compete in the global market and were crushed. Their production methods were old fashioned and much more expensive. They were one of the last manufactures to employ skilled craftsman to make their knives. I think they finally gave up the ghost in the 70's or 80's after they went into receivership and eventually closed their doors. about 10 years ago or so someone decided to reopen the company under the same brand and sell vintage overstock, when that ran out they decided to make new knives and the quality that they were famous for didn't come back. They are branding themselves as a wustof or Henckels type company.
If you can find truly vintage pieces jump on them, but beware of the new pieces being sold as vintage, because they suck. I have several including one with a 16 inch blade that is so well balanced that it feels like an extension of your hand. It takes and holds an edge better than any newer German knife I have used. You can sometime find some on ebay for a great price because people don't know what they have. in short the vintage ones (pre 1980'S) are awesome, new ones not so much.
Hope this helps
I just got a Gustav Emil Ern scimitar 27 from my cousin who used to own an abbatoir. It's brand new with all the stickers (Stainless steel molybdenum alloy...better than ever). Thanks for the information. This was definitely from the 70's since the abbatoir was shut down in the early 80's.
there is some learning curve..like all my red onion cuts turn black
i am also probably going to wet sand the blade clean so i can get a good looking patina started. i had some mis-steps, and left some bits of onion on the blade and started my current patina down the wrong path. (thanks to that patina thread)