An ‘administrator’ is the person who deals with the estate if there’s no will.
You can usually apply for a grant of representation to be the administrator of the estate if you’re the person’s next of kin, eg their spouse (or civil partner) or child.
You can apply if you’d separated from the person but you were still married or in a civil partnership when they died.
You can’t apply for a grant of representation if you’re the partner of the person but weren’t their husband, wife or civil partner when they died. You’re also not automatically entitled to any of your partner’s estate.
The law decides who inherits the estate if there’s no will.