In Anglo-Saxon England (the time before the Norman Conquest of 1066) the highest rank beneath that of the king was ealdorman. The first ealdormen were referred to as duces (the plural of the original Latin dux) in The Anglo-Saxon Chronicle. After the Viking (Danish) invasions and the subsequent establishment of the Danelaw in the 9th century (the part of England ruled by the Danes), ealdorman was replaced by the Danish eorl (later earl).
In Anglo-Saxon England earls were the only title of nobility. These men essentially served as royal governors and ran the counties as personal representatives of the king. By the 12th century the Norman earls were the equivalent of the continental count (which is why the wife of an earl is called a countess; the title is also related to the word county, as earls were originally the owners or controllers of counties). By the 13th century earls ranked just below the king, but they were not necessarily more powerful or wealthier than other noblemen of lower ranks. By the 14th century the creation of a new earldom involved a special public ceremony where the king personally tied a sword belt around the waist of the new earl, emphasizing that the earl’s rights came directly from the king.
The Earldom of Shrewsbury, created in 1442 for John Talbot, is the premier earldom of England, though technically the Earldom of Arundel is older. Created circa 1138 for the Norman baron William d’Aubigny, the Earl of Arundel is today a courtesy (subsidiary) title of the dukes of Norfolk. Thus, the earls of Shrewsbury are the premier earls of England if one defines such a thing as a free-standing title in its own right.
An earl’s wife is a countess; she is address as “lady”; an earl is addressed as “lord.”
A British earl wears a coronet (a gold-plated metal circlet with faux jewels pressed from the metal) that features eight strawberry leaves and eight silver balls (known as “pearls” and presented on raised stalks). See above for an image of an earl’s coronet. The coronet is worn only at coronations.
Image of an earl’s coronet by Sodacan / Wikipedia. Image licensed under the Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic, and 1.0 Generic licenses.