Atlas Copco is a major Construction and industrial tool manufacturer based in Sweden. In the late 70s or early 80s they wanted to get into the electric power tool market. They purchased Milwaukee in the USA, and the power tool division of AEG in Germany. After the purchase tools from AEG were rebranded and sold under the Milwaukee brand in the USA and some Milwaukee tools were likewise sold under the AEG brand in Europe. Tools from both brands were also rebranded and sold as Atlas Copco as well. One of Atlas Copco's major product lines are tools for assembly production. The Atlas Copco production screwdrivers used the same battery system as AEG and Milwaukee.
In the USA, the AEG line seems to have been geared to Industrial use so there was a wider variety of specialty cordless and other tools than what was available from Milwaukee. The Cordless AEG and Atlas Copco tools also were available with better chargers and batteries.
When Atlas Copco decided to get out of the power tool buisiness they sold the AEG Milwaukee buisiness to TTI, the electrical component manufacturer that owned Ryobi. TTI decied to turn Milwaukee into the high end brand, and repositioned AEG as a mid tier brand. A few of the Industrial AEG designs are still manufactured though, and AEG/Milwaukee motors are still supplied to outside tool manufacturers who don't make their own motors.
There are at least two tools manufactured by AEG that were sold by Milwaukee prior to the purchase by Atlas Copco, so there might have been some connection between the companies before the Atlas Copco purchase.