Jiraiya was a student of the Third Hokage and the sensei of the future Fourth Hokage. Jiraiya is also one of the Three Legendary Sannin, together 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" meaning "perverted hermit". Although he is kinda stupid and funny, he truly is a master ninja. He teaches Naruto to control his two chakra types and to summon toads. He also taught Naruto the Rasengan.
As such, Jiraiya's fighting techniques are mostly defensive. His "Underworld Swamp" immobilizes a large amount of ninjas 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 Gamabunta.
There might be a good reason why he specializes in defensive techniques, and that is because he is 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 very rarely caught.