Who is ero-sennin?

Answer 1

Ero-sennin (translated pervy sage or perverted sage/wiseman) is Naruto's nickname for Jiraiya, his last human sensei and also the one who trained his father, the 4th hokage. Naruto mastered the sage arts from the elder toad. Jiraiya is also Naruto's godfather, but Naruto is more like Jiraiya's grandson as mentioned by Jiraiya.

Notes:

1. Naruto is one of the few male characters still alive who shows any interest in the opposite sex, so there is some hope of him becoming perverted. Sexy Jutsu!!!

2. As far as character development goes; Naruto has surpassed, in one way or another, Kakashi, the 4th Hokage, and now even Jiraiya. Expect him to become godly in the next few chapters and then "broken" when he studies his father's sealing scrolls. This manga will climax soon hopefully.