The history of the dogs that eventually made up the Sealyham is a bit of a mystery, but Capt John Edwards of Sealyham is the one that introduced the breed as it is known today. They were used primarily as gaming terriers.
This is a fairly calm breed, especially for a terrier. They are happiest with a good game of chase or a sizable area to investigate. They can be diggers, but are also playful and outgoing.