Ryan O'Reilly has always been considered a great leader. Not only in the locker room, but he plays a style of game that every coach wants to have in their lineup. Not only does he produce points, he leads by example by playing a great two-way game in both ends of the ice and also never had more than 18 penalty minutes in a season, demonstrating how much sportsmanship this player has.
When the Maple Leafs acquired O'Reilly, he was the captain of the St. Louis Blues. This season, the Maple Leafs leadership core consisted of John Tavares as Captain, and career Maple leafs Auston Matthews, Mitch Marner and Morgan Reilly as the assistant captains.
The final game of the Maple Leafs season, Matthews and Marner were healthy scratches, which left an opening for someone to wear the 'A' for the team, and apparently they both offered it to O'Reilly.
Wearing a letter for a team is an incredible honour, especially for an 'Original 6' team like Toronto. O'Reilly though, wanted someone else to have that honour: