The Grenadiers

A Grenadier was originally a specialized soldier, first established as a distinct role in the mid-to-late 17th century, for the throwing of grenades.
As grenade usage declined significantly in the early 18th century, a fact that can be attributed to the improved effectiveness of massive infantry line tactics.
However, the need for elite assault troops remained.
So the already existing Grenadier companies were used for this purpose. Making the Grenadiers the elite troop of the infantry.
As above average physical size had been considered important for the original Grenadiers, especially height and strength remained the basis of selection.

To be a Grenadier you would have had a minimum of 4 years of service and have participated in at least 2 of the following campaigns:

Ulm
Austerlitz
Jena
Friedland

Newly formed regiments and battalions didn't have Grenadiers as they not had been in enough combat.

The 105e Régiment d'Infanterie de Ligne