All living authentic examples can trace their ancestry back to a small number of his original Ilmer Sealyham dogs, and resulting Lucas Terrier progeny.

[2] Sir Jocelyn Lucas, 4th Baronet, a well-known huntsman and Sealyham Terrier breeder in the first half of the 20th century, was disappointed with the direction the Sealyham Terrier was headed since its appearance in conformation shows, especially large heads and heavy shoulders.

Lucas Terriers possess even temperaments and have been bred for companionship, although there are an increasing number of working Lucases to be found around the world.

The standard states that they be friendly, without aggressive tendencies, and not fearful or nervous, while retaining the usual terrier traits.

Pale-shaded or white examples are frequently mistaken for Sealyham Terriers, although their size (typically 11-17 lbs.