Blofeld is the leader of Spectre, the organization that Bond fights against in his first several movies. Blofeld is in several movies but is not shown in his entirety until You Only Live Twice when he finally reveals his face as that of Donald Pleasance with a scar across his face. He later appears again and is portrayed by George Zucco in On Her Majesty’s Secret Service. George Zucco is a good, menacing actor, who frequently portrays villains, but between the two I prefer Donald Pleasance as Blofeld. Blofeld later appears in Diamonds Are Forever, but is kind of hammy and goofy. After that he makes a brief appearance in the beginning of For Your Eyes Only, but is dispatched of pretty quickly.
Blofeld is the quintessential Bond villain and his Spectre organization not only had some of the classic Bond villains but was also the quintessential Bond villain organization. They lasted through out four of the first five Bond movies. Also, Donald Pleasance is a great actor. He played Dr. Loomis in my favorite horror movie series called Halloween and played one of the characters in another great movie called the Great Escape. Donald Pleasance proves once again how great of an actor he could be sometimes as the menacing, cold blooded Blofeld in You Only Live Twice, the most classic of all the Blofeld appearances.