I just read that a person who envies is called an 'envier'. What is a person who is being envied called?
Actually, that would be the envy of the envier...
1.1 (the envy of) A person or thing that inspires envy.
'France has a film industry that is the envy of Europe’
idol also comes close, but does not have the element of bitterness of envy.
A person or thing that is greatly admired, loved, or revered.
‘a soccer idol’
"Envier" is very uncommon, btw.
Just as you can use the phrases the dead, the desired, or the forlorn, you can also refer to the object of envy as the envied.
In the book Cinderella and Her Sisters: The Envied and the Envying, Ann and Barry Ulanov say (emphasis mine):
In personal terms, the envied experiences transmutation from subject into object as being utterly cast adrift. It is as if one has become a garbage can into which all the tainted stuff of the envier can be dumped. The envied one is reduced to the envier's projections. Human relationship with the envier is blocked, an bond of sympathy or understanding severed.
In the book Thousand and One Nights, one of the stories is "The Story of the Envier and the Envied." It starts as follows (emphasis mine):
KNOW, O my master, that there was a certain man who had a neighbour that envied him; and the more this person envied him, so much the more did God increase the prosperity of the former. Thus it continued a long time; but when the envied man found that his neighbour persisted in troubling him, he removed to a place where there was a deserted well; and there he built for himself an oratory, and occupied himself in the worship of God. Numerous Fakirs 1 assembled around him, and he acquired great esteem, people repairing to him from every quarter, placing firm reliance upon his sanctity; and his fame reached the ears of his envious neighbour, who mounted his horse, and went to visit him; and when the envied man saw him, he saluted him, and payed him the utmost civility.
In the Psychology Today article "Being Envied Is Not Enviable," Mary C. Lamia says (emphasis mine):
Although envy can motivate someone to damage the position of the person who is envied, either in their imagination or in reality, their envy can also make them work harder in order to attain what the envied person has.