Noble Hierarch — ruling 1

If you declare exactly one creature as an attacker, each exalted ability on each permanent you control (including, perhaps, the attacking creature itself) will trigger.

Noble Hierarch — ruling 2

You must attack with exactly one creature for exalted abilities to trigger. Exalted abilities won't trigger if you attack a player with one creature and a planeswalker with another, for example, or if you attack with two creatures but one is removed from combat.

Noble Hierarch — ruling 3

Some effects put creatures onto the battlefield attacking. Since those creatures were never declared as attackers, they're ignored by exalted abilities. They won't cause exalted abilities to trigger. If any exalted abilities have already triggered (because exactly one creature was declared as an attacker), those abilities will resolve as normal even though there may now be multiple attackers.

Noble Hierarch — ruling 4

In a Two-Headed Giant game, a creature “attacks alone” if it's the only creature declared as an attacker by your entire team. If you control that attacking creature, your exalted abilities will trigger but your teammate's exalted abilities won't.

Noble Hierarch : règles, fonctionnement et interactions (MTG)

Noble Hierarch is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.) : Add , , or .

How it works : Noble Hierarch

Original English text — Wizards of the Coast / Scryfall

#1August 7, 2020· Wizards of the Coast
If you declare exactly one creature as an attacker, each exalted ability on each permanent you control (including, perhaps, the attacking creature itself) will trigger.
No other card is named in this ruling.
#2August 7, 2020· Wizards of the Coast
You must attack with exactly one creature for exalted abilities to trigger. Exalted abilities won't trigger if you attack a player with one creature and a planeswalker with another, for example, or if you attack with two creatures but one is removed from combat.
No other card is named in this ruling.
#3August 7, 2020· Wizards of the Coast
Some effects put creatures onto the battlefield attacking. Since those creatures were never declared as attackers, they're ignored by exalted abilities. They won't cause exalted abilities to trigger. If any exalted abilities have already triggered (because exactly one creature was declared as an attacker), those abilities will resolve as normal even though there may now be multiple attackers.
No other card is named in this ruling.
#4August 7, 2020· Wizards of the Coast
In a Two-Headed Giant game, a creature “attacks alone” if it's the only creature declared as an attacker by your entire team. If you control that attacking creature, your exalted abilities will trigger but your teammate's exalted abilities won't.
No other card is named in this ruling.