Deck Leader

Deck Leader is a position a monster card can hold in the Playstation 2 game Yu-Gi-Oh! The Duelists of the Roses. The Deck Leader serves as your mobile base, representing your Life Points, summoning monsters from the hand, and setting magic and trap cards from the hand.

Promotion
When you are given your deck by Simon, you have chosen your Deck Leader. As you duel, cards you use frequently, being summoned, attacking, defending, inflicting critical hits, etc. will earn that monster XP. This XP cannot be seen, but after enough duels, at the end of your duel, you will get a prompt telling you your card has been promoted. All monsters in your deck can be promoted, not just your current Deck Leader. This means you can theoretically have any card be your Deck Leader, eventually.

Demotion
In a similar way to promotion, loosing duels can get your Deck Leader demoted. They will go down 1 Rank.

Rank
All monster cards start with no Rank. When they get their first promotion, they are ranked Second Lieutenant (2LT in the game's shorthand).

No Rank Second Lieutenant First Lieutenant Captain Colonel General

Leader Ability
Deck Leaders have special effects called Leader Abilities. Your first Deck Leader has a Leader ability right away. Other monsters cards who become promoted can earn Leader Abilities, though when this happens and how is not explained in the game. Various Leader Abilities include:

Increase Attack for Same Type Friendlies Increased Movement Level Cost Reduction for Summoning Same Type