Fra Pandolf is the name of the painter who painted the famous portrait of the Duke's last Duchess that is being surveyed by the Duke and his guest during the poem. We are told how "busily" Fra Pandolf's hands worked to create this masterpiece. However, it is also important to note that Fra Pandolf, who is a character that we never meet in person during the course of the poem, is also used to signify the obsessive jealousy of the Duke. Note where else Fra Pandolf occurs in this poem:
Sir, 'twas not
Her husband's presence only, called that spot
Of joy into the Duchess' cheek; perhaps
Fra Pandolf chanced to say, "Her mantle laps
Over my lady's wrist too much," or, "Paint
Must never hope to reproduce the faint
Half flush that dies along her throat." Such stuff
Was courtesy, she thought, and cause enough
For calling up that spot of joy. She had
A heart--how shall I say?--too soon made glad,
Too easily impressed...
The Duke imagines that even in response to Brother Pandolf's innocent compliments his last Duchess had her interest in other men kindled. The fact that Fra Pandolf was probably part of a religious order and therefore celibate emphasises the jealous nature of the Duke. He imagines his last Duchess to have "looks" that "went everywhere," especially, it is implied, to other men apart from himself. Thus we can argue that this character is used to emphasise the character of the Duke himself and his obsessive jealousy.