Jarlabanke Ingefastsson was likely a hersir, a chieftain or military commander, of a hundred, which was an administrative division of a hundred men (and their families). He would have been responsible for organizing military support in times of war. (Hundreds were used extensively in Europe, and even in the United States: Delaware, New Jersey, and Pennsylvania used hundreds in the 17th century.)
Jarlabanke likely was very well-off financially thanks to the Danegeld, the practice of being paid off by England to stop attacking it. Another source of revenue would have been from men of his hundred being paid as mercenaries in the Varangian Guard and fighting in Kievan Rus.
He used them to commemorate fallen family members and comrades, and public works. The inscription for the one pictured reads:
Jarlabanki had these stones raised in memory of himself while alive, and made this bridge for his spirit, and (he) alone owned all of Tábýr. May God help his spirit.
Tábýr is modern Täby. There is a bit of controversy based on an Old Norse verb over whether he actually "owned" or was simply a chieftain appointed by the King of Sweden.
The bridge mentioned is actually a causeway. There are three other stones raised to give him credit for constructing roads and bridges.
There are two Jarlabanke Runestones that mention men who traveled abroad. One of them is broken and now shows only the fragment Hann ændaðis I Grikkium, "He ended [died] in Greece." This is considered part of a subset of stones referred to as Greece Runestones, which will be our next (and final) look into the practice of raising runestones.