Michael Prodger at The New Statesman:
One of the many complications that make the Bruegels the most confusing clan in art is the letter H. Pieter Bruegel the Elder, the founder of the dynasty and its greatest artist, was the painter of such celebrated works as The Hunters in the Snow (1565) and The Tower of Babel (1563). Contrary to the elegance and elevating tenets of the Italian Renaissance, he made the peasant life of the Low Countries his subject, in all its scatological, rambunctious and therefore human detail. In 1559 he dropped the H in his surname and started signing in Roman capital letters – Brueghel becoming the rather more stately Bruegel.
Bruegel had two sons, Pieter and Jan, aged four and one at the time of his death in 1569. Both became painters, too, and as their careers took off Pieter the Younger reinstated the H his father had discarded (though in later life, to add to the disorder, he reversed the order of the U and E) and it remained the moniker of the innumerable painting Brueghels who followed. Rather more confusing than this alphabet jiggery-pokery, though, is the sheer number of painters in the dynasty – some 15 blood relations over the course of 150 years, before a plethora of apprentices, collaborators and intermarriages is factored in.
more here.