Enter Happosai, the Lustful Lecher!
Kyukyoku no Ero Yokai Happosai
"A perverted old man named Happosai appears before Akane. He turns out to be the master of both Genma and Soun. While the two old pupils panic, Happosai appoints Ranma as his heir and decides to stay at the dojo indefinitely. " (source)