Most likely a large part of why Sith do this is because they feel that they are truly different people then they were before, and do not want to continue using the same names. Throughout the Star Wars films, there is an emphasis on the fact that when someone falls to the Dark Side they become someone different then they were before, from a certain point of ...
Yoda couldn't beat Palpatine possibly because he:
Was only fighting to escape (extremely unlikely)
Already mentally in a weaker position due to the deaths of his fellow Jedi comrades
Was overall weaker at lightsaber duelling
There are two possible "answers":
Disney Canon: Not enough info for a definite answer, but Sidious was likely just Sidious.
Legends: A definite answer is still not fully available, but Sidious was almost certainly just himself.
Not surprisingly, there is little information about this available at all in Canon. The closest comes from the this ...
The notion of the Sith, as an order of evil Force users, was introduced in The Phantom Menace. The name "Sith" is much older, appearing in early screenplays for The Star Wars and first published in the Alan-Dean-Foster-ghostwritten Star Wars novelization. However, in those early appearances, "Lord of the Sith" was an unexplained title. (In fact, the ...
As early as 1973:
Until the recent GREAT REBELLION,
the JEDI BENDU were the most
feared warriors in the universe.
For one hundred thousand years,
generations of JEDI perfected their
art as the personal bodyguards of
the emperor. They were the chief
architects of the invincible
IMPERIAL SPACE FORCE which expanded
the EMPIRE across the galaxy,
from the ...
That question is fully answered by a retcon I really quite liked in The Rise of Skywalker.
When a Sith slays their master they become possessed by the spirit of their master, plus all the previous Sith in the chain, including all their previous experience, memories and knowledge. This explains how he was able to resurrect himself:
That's why he wanted Luke ...
Baby Yoda does this in The Mandalorian S1E7. There is a deep gash in someone's arm and, using The Force, Baby Yoda heals it completely (as in the flesh is fully restored). It might not sound like it fits (it wasn't life-threatening), but it tied into Rise of Skywalker when
Darth Sidious uses the Force to save Vader on Mustafar
From the Return of the Sith novelization by Matthew Stover, Chapter 21:
The Sith Lord lowered the limbless man tenderly to the cool ground above, and laid his hand across the cracked and blackend mess that once had been his brow, and set his will upon him.
Live, Lord Vader. Live, my apprentice.