Some characters are highly change from each timeline but some don't thank to their chronokinesis and their understanding of it as they know about other timelines.

Known people are who the same across timelines

Professor Paradox
He deeply aware the multiple timelines, he even aware of another version of himself native to the Ben 10 multiverse.

Chronians, Chronosapiens, and Celestialsapiens
These species are deeply aware and remain the same across different timelines but mostly used by villains like Eon, Maltruant, and Vortech.

Time Eater
It deeply have the power to do so as he brought Crisis City back and indirectly caused the timeline of Classic Sonic to bridge away from the main Sonic timeline in Generations.

Mephiles The Dark
Revived by the Time Eater, he now become a living paradox as no matter how many times he died, he always come back. In fact, he's the reason there are many different timelines as he either directly or indirectly change Cinos' fate.

Time Force and Hyper Force Rangers
These time traveling Rangers always come back to the past in hope everything is okay as they try not to fully meddle with the past.

Possibly more that I can list like various gods from Power Rangers, Gargoyles, etc,