Sensational Hydra was a HYDRA leader too flamboyant to be called the traditional "Supreme Hydra" so he got the "Sensational Hydra" moniker.
Sensational Hydra ordered several attacks on Captain America, who defeated his men, but it was all part of Sensational Hydra's plan to raise Captain America's iconic status in the public. Sensational Hydra and two of his lackeys turned out to be Skrulls who got stranded on Earth, and now that Cap was so popular, Sensational Hydra supplanted him.
Sensational Hydra as Cap organized a press conference to tell one of each twenty people was a Skrull in disguise, and betrayed his two lackeys to support the charade. This creates a mass panic as everybody tries to kill anybody suspected of being a Skrull spy.