Jiraiya

Jiraiya was a student of the 3rd hokage and also was the sensei of the future 4th hokage. Jiraiya is one of the Three Legendary Sennin's, with Tsunade and Orochimaru. He is the "Rock" as the three are heavily based off the "Rock, Paper, Scissors" game, or also known as Janken. You first see him peeping in the women bathing place to "collect material". Naruto then gave him his nickname "Ero-sennin". Although he is kinda stupid and funny, he truly is a master ninja. He teaches Naruto to control his 2 chakras and to summon frogs. As such, Jiraiya's fighting techniques are mostly defensive, His "Underworld Swamp" immobilizes a large amount of ninja's in a marsh, and his "Underworld Spines" defend him from any physical attack. He mostly relies on his summoning frogs to aid him, though he rarely summons Gama Bunta. There might be a good reason why he specializes in defensive techniques, and that is because he a complete and utter pervert, who writes a series of books known as Icha Icha Paradise, a book Kakashi himself adores. As such, he has grown so adept at peeping he is rarely caught. Also see Ero-Sennin