collected source from all over Johnny’s.news110 which, unfortunately, hasn't been updated since 2006
EDIT: Added with recent compilation of nicknames right below, source: manimani
大野智 Ohno Satoshi
櫻井以外のメンバーからは基本的に「リーダー」と呼ばれている(櫻井は「大野くん」や「智
Other than Sakurai, other members call him “Ri-da- (leader)”, (Sakurai calls him “Ohno-kun” or “Satoshi-kun”). Nino, in his cell phone site diary, calls Ohno “Pan-ya-san (Mr. Bread House)”. Among fans, other than the petname “Oh-chan” which Tomohiro Hara gave, “Ri-da-” is also rather popular. Recently (okay not so recent, this article is rather old already), in Ninomiya Kazunari’s radio show Baystorm, he called Ohno “Sami-”. “When Sami- goes for a meal with ‘big-shots’ he will foot the bill” – says Ninomiya. Pretty often you will also hear “Ojisan (old uncle)” coming from Ninomiya Kazunari. However, Ninomiya also uses this nickname for Aiba Masaki, so it’s hard to differentiate. Although “Ohchan” was actually his nickname during kindergarten days, but now it has been replaced with “Ohno” since losing to “Ohmura-kun” (someone else by the name Ohmura is now having the nickname ‘Ohchan’). Recently, people started switching from “Ri-da-” to “Captain”. When Arashi had a gathering drink (a farewell for Nino who’s leaving for America), with an excuse saying that other groups also call their leaders “Ri-da-”, Arashi members decided that they can’t be the same. It’s just that, does Arashi have some kind of periodic boom or something? They always change the nicknames for each other and we don’t know when they’ll change it again. (Now, “Sami-” isn’t heard at all)