Ma Beagle, based on the real-life gangster Ma Barker, is the mother of the seven Beagle Boys featured on the original DuckTales series (named Bigtime, Burger, Bouncer, Baggy, Bankjob, Bugle/Bebop, and Babyface) and the clan matriarch. She often smuggles hand grenades, chainsaws, and other tools in baked goods which easily pass prison security to help her sons escape from jail.
Although she appears to be more competent than her children, she is always outwitted by Scrooge and his nephews. However, she avoids being arrested in season 1, and in season 2, she takes a more active role until she is finally arrested.
Ma Beagle returns in the reboot series and continues to be the leader of the Beagle boys and as one of the four leading villains alongside Magica De Spell, Flintheart Glomgold, and Mark Beaks. She is more mean and abusive towards her sons in this series. She has a grudge against Scrooge for stealing the deed of her Grandpa Beagle as mayor.
Ma Beagle seems to be the female counterpart of Grandpa Beagle who served as one of the main villains in the Duck comics and seems to be his stand-in in the TV series DuckTales.
Out of all the main antagonists in the reboot, she seems to be the one that appears the least. This might be due to the fact that she's more pragmatic than the rest of Scrooge's rouges gallery, prefering more low-key schemes rather than showing off like Magica and Glomgold do.
Her name is Katherine in the reboot, as it's revealed by Glomgold in the episode Glomtales.