We all know there are numerous animes/mangas out there so it shouldn't be something strange when characters from different animes/mangas look similar but the case of Shans "The Red Haired" and Gildarts clive is especially "Curious". Ignoring the huge fact that both of them have near similar/exact look, they also seem to play a similar role, with each standing as a sort of Father/Role model figure to a respective eccentric major characters in their anime/manga. They both are two of the most powerful characters ever created in manga, with the both of them holding পরবর্তি to the highest post in their manga/anime. Shanks holds the position of one of the 4 emperor's (yonkou) the closest to the highest post PIRATE KING(Kaizoku ou) while Gildarts Ranks above the 10 বছর quest but just below the 100 বছর quest(which seems to be the highest so far). The both of them play a similar role of motivating a major character to get stronger and meet them at the শীর্ষ of their respective worlds(in terms of strength). They both seem to be capable of completely immobilizing strong opponents দ্বারা emitting a sort of fear/intimidation mantra (shanks - haki, Gildarts- raw magic power). Not to mention the little fact that they both became নায়ক to the major characters they motivated দ্বারা saving them from a savage monster at a young age; shanks saving luffy from a sea king and Gildarts saving natsu from a mountain vulcan, both of them seem to have done it without lifting a finger, merely intimidating the monsters with their expression and aura. Both of them seem to have হারিয়ে গেছে an arm, though Gildarts uses a prosthetic arm. There are other similarities but there also happens to be some differences a major one being Shanks is a Drunkard and Gildarts is a Womanizer(but doesn't প্রদর্শনী it like Sanji does).

Don't আপনি find it intriguing that two characters can be so similar.

But one thing is sure, messing with this characters might not be too dangerous but if আপনি mess with their FRIENDS/NAKAMA well....
The picture below says all