The Genesis still struggled in the United States against Nintendo, and only sold about 500,000 units by mid-1990. Nintendo had released Super Mario Bros. 3 in February 1990 which further drove sales away from Sega's system. Nintendo themselves did not seem to be affected by either Sega's or NEC's entry into the console market.[1] Sega's president Hayao Nakayama wanted the company to develop an iconic mascot character and build a game around it as one means to challenge Nintendo's own Mario mascot.[23] Company artist Naoto Ohshima came up with the concept of Sonic the Hedgehog, a fast anthropomorphic character with an "attitude" that would appeal to teenagers and incorporating the blue color of Sega's logo, and Yuji Naka helped to develop the game Sonic the Hedgehog to showcase the character as well as the graphics and processing speed of the Genesis.[24] The game was ready by early 1991 and launched in North America in June 1991.