Partially successful count?
Several men attempted to impersonate the heirs to the House of York after the death of the last Yorkist King: Richard III in England. This was significant because if the claim was true, then the claiment would be the rightful king of England.
The first to do so is Lambert Simnel, who claimed to be the younger of the princes in the tower (sons of Edward IV who were purported murdered by Richard III): Richard of Shrewsbury (the potentially rightful king of England if he were actually alive and his older brother dead). He found considerable support in Ireland, and was used as a figurehead by the Earl of Lincoln to raise a Yorkist revolt against Henry Tudor: with the stated purpose of putting the imposter on the throne. The rebellion was defeated at the battle of Stoke in 1487. Lambert was captured by Tudorist forces, but pardoned due to his young age, and was given a job in the Royal kitchens.
The second person to do was Perkin Warbeck, also claiming to be Richard of Shrewsbury. He found considerable support on the European continent, gaining the public recognizance of his father's sister: Margaret of York. Some other Euopean monarchs also recognized him as "the Duke of York" (the actual Richard of Shrewbury's title). His physical resemblance to Edward IV was considered remarkable by contemporary accounts and some historians suspect he might have actually being an illegitimate son of the late king.
Perkin Warbeck repeated attempted to land in England. Finally in 1497, he landed in Cornwall and raised an army of 6000. But when Henry Tudor sent an army against him, he panicked and fled. He was eventually captured, tortured, interrogated, and put in the tower with Edward of Warwick (another Yorkist heir who would be his cousin if he wasn't an imposter). The two were eventually put to death in late 1499.
I am pulling from memory here, but I believe after the death of Ivan IV, who was the last of the Rurikid Dynasty of Russia, there was eventually an impostor in 1603 that claimed to be Dmitry Ivanovich, who was the son of Ivan IV but died at the age of 8, and ruled as Tsar for several years.
From: Russia and the Russians by Geoffrey Hoskings.
It's not entirely the same, but you could also include Anna Anderson's claim to be Duchess Anastasia of Russia, which a significant number of people believed. Obviously she never ruled, but she was able to leverage some benefits from her act.
Removed, this breaks our rules regarding 'throughout history' questions. Sorry we didn't catch it until it had been up for 7 hours, we're usually much quicker!
Take it with a grain of salt, but I believe Herodotus made a claim that Bardiya (aka Smerdis) was killed by his half or full brother Cambyses II after he dreamed his brother would usurp his throne, only to have a magus impersonate Bardiya, rise up against Cambyses, and take the throne after his death.
This view is disputed, however, and may have been an invention to in part justify Darius' later usurping of Bardiya (real or imposter).