①He’s no longer popular.
②He's no longer in his prime.或He's now past his prime.（已过鼎盛期）
③He had his moments.（曾有过辉煌）
④He's a has-been.（过气人物）
1 a has-been
If you describe someone as a has-been, you are indicating in an unkind way that they were important or respected in the past, but they are not now.
He became famous overnight / at that time, but now he is just a has-been.
2 over the hill
over the hill指风光不再，开始走下坡路。
I don't think of myself as being over the hill yet.
3 a spent force
a spent force指过气、昨日黄花。
释义：Someone who no longer has the power or influence he once had.
The new album is proof that this band is not a spent force just yet.
4 over party
释义：When a trend or a person is over.
He's over party.
She should go to her own over party.