In (one's) heyday phrase
Used to refer to the most successful, popular, or prosperous period of someone or something.
In their heyday, the band sold over 20 million physical albums in less than 7 years.
In his heyday, he earned 5000 dollars a month as a stockbroker.
In its heyday, the ancient village was visited by hundreds of tourists within a day.
The word "heyday" appeared in the late 16th century (denoting good spirits or passion): from "archaic heyday!", an exclamation of joy, surprise, etc.
To be hilarious or enjoyable
"He's a serious person.- Yes, not a barrel of laughter exactly".