In a interview with 1up, lead director of the original Street Fighter Takashi Nishiyama confirmed that the concept behind the Hadoken technique comes from 1970s anime Space Battleship Yamato, in which the titular battleship has a weapon called the "Hadōhō" (波動砲, "Wave Motion Gun/Surge Cannon"). He also confimed that Ryu's name comes from the first Kanji used for Takashi's name (隆), which can also be read a "Ryu".
Contributed by ZpaceJ0ck0