Ngawang Lobsang Gyatso, the 5th reincarnation of the Dalai Lama lineage. Better known as the "Great Fifth", he was the first major reformer of the Tibetan political system following a series of internal conflicts between rival sects of Vajrayana Buddhists. The civil war was put down through an alignment between the Mongol military and the monastic leaders of the Gelugpa faction.

His unexpected death came at a time of awkward political interactions with the rising Qing Dynasty, as well as in the middle of a war between the Mughal and Ladakh empires in the South. The complexity of the political situation convinced the Great Fifth's regent (desi), Sangye Gyatso, that his death should be hidden from public knowledge while he simultaneously raised the 6th Dalai Lama reincarnation as another State secret. This went on four 14 years.

Though I cannot find a source for the following claim, I recall that his cover story was that the Great Fifth had retreated to performing an extended feat of advanced meditation for all that time. I am sure that one of the various experts in Tibetan or Buddhist history on this sub may be able to fill in the gaps created by my inexperience with the historical material.

Source:

One Hundred Thousand Moons | Chapter Eight. Conflicts Between The Sixth Dalai Lama, The Regent Desi Sangyé Gyatso, And Lozang Khan

I’m sure there are many many examples of this. On reading this question, however, the first ones that came to mind were either Lambert Simnel (masquerading as Edward, Earl of Warwick) or Perkin Warbeck (masquerading as Richard, Duke of York). I accept that these cases don’t quite fit the brief as neither were ‘king’. Although, I hope you’ll agree that they are equally, if not more so, valid examples of using the dead to further your own legitimacy.

First, some context on these events and why I have raised them together. In short, they are essentially the same thing, happening twice.

I’m going to presume most people are faintly aware of the Wars of the Roses, not least because explaining it fully would require more posts than I’m willing to make. Essentially, two branches of the same family, the Plantagenets, were locked in a long and bloody struggle to secure the Kingdom of England for their respective branch. These branches, either York or Lancaster, come from the titles possessed by each branch (don’t be confused into thinking that they were ‘from’ or represented the area in any real way) and had been at each others throats since the death of Edward III in 1377 from whom they all descended.

By the 1480’s the Yorkist faction were the current incumbents of only 15 years, having held the throne in the person of Edward IV and then Richard III. The leading Lancastrian claimant, Henry Tudor, was exiled, licking his wounds and biding his time. Richard was an unpopular king, not least for the murky atmosphere that surrounded his accession. In 1485, Henry successfully leveraged this unpopularity to his advantage, landed in England with a small army, killed Richard at Bosworth and took the throne. He then married Elizabeth of York, eldest child of Edward IV, niece to Richard III and a senior Yorkist. This supposedly ended the feud, with the uniting of the two branches. The Tudor rose of white on red symbolised the idea of all future royal children being both Yorkist and Lancastrian. And that was that.

But not for long! Of course, the Yorkist faction were not pleased about the Lancastrian ascendancy and in true medieval fashion went abroad to seek aid in placing a Yorkist claimant on the throne. In particular, Margaret of York, dowager Duchess of Burgundy, would support dozens of attempts to unseat Henry. True to form, other powers such as France and the German princes also promise support at one time or another. And so we turn to their first attempt, Lambert Simnel.

He was a boy from Ireland who just happened to have the misfortune of looking a bit like Edward, Earl of Warwick and knowing Richard Symonds. Symonds was a priest and court tutor, who noticed the physical similarity of the two boys. His motivations are ultimately unknown, so I won’t go into them here, but he eventually brings the boy to Earl Kildare, an Irish grandee and known Yorkist in 1487. Now, some important things to know about Edward: He was another nephew of both Edward IV and Richard III. He was 10 in 1485, which was when he was captured by Henry Tudor (now Henry VII) and imprisoned. Earl Kildare knew this and, sensing opportunity, proclaimed that Lambert was in fact the boy Edward.

The important things to note here is that everyone involved here, the Yorkists, Lancastrians, Kildare, Symonds and certainly Simnel all knew that Edward was in the Tower of London. Nonetheless, the Yorkists rallied around Simnel and he was coronated ‘Edward VI’ in Dublin. However, not one month later, the Simnel rebellion was defeated at Stoke by the King. Scores of Yorkists were either killed or captured, not least the Earl of Lincoln, who had been Richard’s appointed successor and Thomas Fitzgerald, younger brother of Earl Kildare. Symonds was spared execution for being a clergyman, but got life imprisonment. Simnel himself was employed at in the royal kitchens and lived a natural life. So a resounding failure for the Yorkist cause, no? Also, not really a case of pretending a king was still alive* to claim legitimacy, I hear you cry. Well, allow me to introduce the wonderfully weird Perkin Warbeck.

(Story continues in the comments)

There was a situation like this in Brazil, but it didn’t work out.

In the dictatorship the presidential election were not voted by civilians, it was decided by “Colégio Eleitoral” which was composed by congressmen and delegates of legislative assemblies, and in 1985, for the first time since the dictatorship started, a civilian won the election. It was Tancredo Neves, everyone was hopeful, but little did they know that he wouldn’t be able to assume the presidency.

Tancredo Neves was 75 years old and was making a pretty big campaign, the doctors advised him to take some rest, but he didn’t. He used to say “do everything to me, but after the elections!”. The vote counting happened and he won, but he died due to some complications in a surgery he had to have.

The party tried to hide his death because his vice-president candidate was a military and the victory of the civilians would have been for nothing. They tried to hide till the day that he would formally act as a president so then they could replace him for someone else. But they didn’t succeed. People discovered that Tancredo Neves had died and a wave of devastation filled the brazilian population.

Some people say that Tancredo was actually assassinated, that his death was intentional and it was a medical negligence case. This argument is supported by the fact that only a few people knew about his death and no snitch was found, so there’s was no way people would “magically” discover about it. So some say it was all a plan of the militaries when they found that Tancredo won.

These allegations are not confirmed till this day because a lot of documents from the dictatorship were destroyed and the acts of the militaries were forgiven (by the law).