It started with the top image. An artist called Blue posted a drawing of a Black Widow and Hawkeye cover with the poses swapped. Blue then issued a challenge to other artists: replace the female characters in other comics with Hawkeye. These are just a few examples of what happened next.
Stan Lee, co-creator of Spider-Man, the Fantastic Four, the X-Men and more, turned 89 years old today. Lee first broke into comics in 1939 after graduating high school at age 16. His uncle helped him become an assistant at Timely Comics, which would later become Marvel. His first writing to appear in a comic book was a text filler page in "Captain America" issue #3. Since then he has helped create numerous beloved characters, helped reform the Comics Code, and challenged conventional ideas of what a superhero could be. Happy birthday, Stan. Excelsior!