"I am Dr. Ivo Robotnik, the greatest scientific genius in the world!"
Hear me out - I realize Dr. Robotnik (or Eggman, as he is referred to nowadays) is not among the most successful of villains. Sonic has foiled every single one of his plans, from his earliest robotic creations to his most recent time-travelling beast. But there's no denying how iconic the goofy main antagonist of the Sonic the Hedgehog franchise is.
Robotnik has never been known for subtlety. His classic hover chair accommodated a number of attachments, from spiked wrecking balls, to drills, to hydro cannons. His floating Death Egg fortress was one of his earliest creations that reached mammoth proportions. In Sonic Adventure 2, he reactivated the lost colony ARK, which was revealed to have a giant cannon capable of shattering half of the moon, and that just so happened to bear a striking resemblance to his own visage. Even the Egg Dragoon, though considerably smaller than the other two, is an ostentatious mecha unit loaded with every imaginable form of ammunition to serve as overkill in taking down one hedgehog.
Some of his more successful endeavors include the creation of Metal Sonic, and the occasions where he turned to Knuckles, Chaos, and Shadow as his ever-powerful number one fighters. Through Chaos, Robotnik managed to acquire each and every one of the Chaos Emeralds, though things went south once Chaos morphed into his uncontrollable perfect form. Shadow, on the other hand, proved much more loyal to Robotnik for the majority of Sonic Adventure 2, even continuing his search for the Master Emeralds as he questioned his purpose late in the game.
Probably the two instances Robotnik came closest to victory over Sonic were during the events of Sonic Adventure 2 and Sonic Generations. His plans in Sonic Adventure 2 would have succeeded, had he not misunderstood his grandfather's legacy. In Sonic Generations, Robotnik (both his past and present selves) used the Time Eater to erase history and every instance of Sonic's victory over him. As a side effect, all of Sonic's friends were locked away in various places from his past journeys. The thing Robotnik had not counted on was the fact that, without any measure of time present, the two versions of Sonic were able to move back and forth freely, and this allowed them to quickly gather the Chaos Emeralds to go Super Sonic on the Time Eater.
Robotnik's victories may be small and limited - often they are through the actions of his creations and subordinates. But he certainly is persistent, and is determined to someday defeat the famous blue hedgehog. His methods can be a bit ridiculous, but you have to give the man credit for his style.
Yes, it's cheesy music from the early 2000s. But I love how catchy Eggman's theme from Sonic Adventure 2 is - very befitting of someone who enjoys tooting his own horn so frequently.