The sitter, Ludovico Terzi, was a prominent churchman in Bergamo. The Terzi family came from Sforzatica, near Bergamo.
Having studied law (probably at Padua from before 1537 until 1540) Ludovico was appointed apostolic protonotary at an unknown date, and was recorded as a canon of the cathedral in Bergamo from 1539 until 1582. He probably died in 1583. He is identified by the letter he holds in his left hand.
This painting would appear to show a man in his mid-40s and has accordingly been dated in the early1560s.
It was unusual for Moroni's sitters not to look at the beholder.