the.com/grand marshal

means The honorary leader chosen to head a parade or ceremonial procession, usually for prestige rather than any actual organizing duty.

from A borrowing from military and court titles — 'marshal' traces back through Old French 'mareschal' to a Germanic root combining 'horse' and 'servant,' originally meaning someone who tended horses, a lowly stablehand. Over centuries the title climbed the ranks, attaching itself to high military and royal officials ('Field Marshal,' 'Marshal of France'), so that by the time it reached parade-ground use, it had traveled from stable boy to supreme commander — 'grand' simply piling extra ceremonial weight onto an already inflated word.