Jesse's surname changed from Cochran to Katsopolis after Full House season one.
John Stamos played Jesse, who was introduced in the first season as Jesse Cochran. The character was Danny Tanner's brother-in-law and a musician who moved into the Tanner home with Joey Gladstone to help raise Danny's daughters.
After the first season ended, the producers changed his surname to Katsopolis to better reflect the character's Greek heritage. The new name was used beginning with season two, and Jesse became widely known as Jesse Katsopolis for the rest of the original series.
The change is sometimes mistaken for a character replacement because the season-one credits and later episodes use different surnames. It was the same character, played by the same actor; only the surname and related family background were revised.