Any person who is very dear to people in general is called a popular man.
As for Kṛṣṇa's popularity, there is a statement in the First Canto, Eleventh Chapter, verse 9, of Śrīmad-Bhāgavatam, that deals with His returning home from the capital of Hastināpura. While He had been absent from Dvārakā at the Battle of Kurukṣetra, all the citizens of Dvārakā had become morose. Then, when He returned, the citizens joyfully received Him and said, "Dear Lord, while You were absent from the city, we passed our days in the darkness of night. As in the darkness of night every moment appears to be a long duration of time, so while You were gone every moment appeared to us like millions of years. Your separation is completely unbearable to us." This statement shows how popular Kṛṣṇa was all over the country.
A similar incident occurred when Kṛṣṇa entered the arena of sacrifice arranged by King Kaṁsa for His death. As soon as He entered the place, all the sages began to cry, "Jaya! Jaya! Jaya!" (which means "Victory!"). Kṛṣṇa was a boy at that time, and all the sages offered their respectful blessings to Him. The demigods who were present also began to offer beautiful prayers to Kṛṣṇa. And the ladies and girls present expressed their joy from all corners of the arena. In other words, there was no one in that particular place with whom Kṛṣṇa was not very popular.