True polymorph can turn a creature into another creature. When it does so, the creature "retains its alignment and personality", although its other statistics change.
However, true polymorph can also be used to turn an object into a creature, and a corpse is an object. The portion of true polymorph which covers turning an object into a creature does not mention any retained personality or alignment, which is sensible because objects typically don't have a personality or alignment.
Thus the question: If Creature A dies, then their corpse is true polymorphed into Creature B, does Creature B retain the personality and/or alignment of Creature A?
(Note: I have used true polymorph as the sole example because I haven't found any other spell that can be used in a similar way. If there is a spell I've missed, feel free to answer with regards to that instead or as well.)
Best Answer
No. A corpse does not have a personality.
Even though the corpse is formerly Creature A's body, the remains no longer have any personality. When the corpse (read object) is transformed into a creature, it is no different than a slab of kraken meat. It follows the object to creature spell variation. Other than Creature B's friendliness, there is no mention of its personality so it must be decided by the GM:
Personally, I would treat it like a regular monster and use the guidance in the Monster Manual to decide on what type of personality it would bring with it.