Lord

The Lord (Junior Lord in Seisen no Keifu) is arguably the most important class on the battle field. In every Fire Emblem game, except in Gaiden and Radiant Dawn, a Lord will represent your main character(s), whoever they may be. Unlike other classes, Lords have no real generalization, as their unique styles and abilities change depending on which Lord(s) is featured within the game. It should also be noted that should your Lord be killed on the battle field, you will automatically lose the game.

Combat
While it is incredibly important to protect your Lord, for fear of an instant defeat, for no reason should you keep them off on the sidelines while your other characters do the work. Lords are usually incredibly capable fighters and players are forced to bring them onto the battlefield for every fight. For no reason should their skills be dulled when taking on the later enemies of the game. They usually use swords, but there are exceptions (Hector, Ephraim). Because the Lord classes changes from game to game (Lord to Lord) no general strategy can be offered other than to find a way to make use of their abilities properly.

Promotions
Every Lord is different, their promotions share the same trait. Different Lords are promoted to different Lord classes, each one specializing in their own fields of combat. Lord promotions are often reached by obtaining a certain level or using a special item after reaching that level. It should be noted that early Fire Emblem games do not have Promotions for Lords, the first game to feature this was Fire Emblem: Seisen no Keifu. In Fire Emblem: Thracia 776, Leaf promotes to Prince (his Seisen no Keifu class) upon retaking Lenster. In Fire Emblem:Fūin no Tsurugi, Roy has his class changed to a Master Lord after receiving the Sword of Seals. In Fire Emblem: Rekka no Ken, Lords must be at least level 10 to use the Heaven's Seal to upgrade to the next class. In Fire Emblem: the Sacred Stones, both Lords are given the option to use the Solar Brace/Lunar Brace to become a Great Lord.

Gaiden
There isn't a lord class in Fire Emblem: Gaiden. Alm is technically a Fighter, while Celica is a Priestess.

Path of Radiance/Radiant Dawn
In Path of Radiance, Ike is the clear-cut Lord character, but is the first Lord character that is not of noble birth. However, throughout the course of the game, he is introduced into nobility, and this event marks his promotion to Lord proper.

In Radiant Dawn, just like in Gaiden, there isn't a Lord class, however the people who fulfill the Lord character are Micaiah and Ike,(Elincia, Geoffrey, and Tibarn are only temporary leaders.) but if one of them die, it is a game over. However, even though other people's deaths result in game overs it is not for the entire chapter,(Dorcas' wife in Chapter 3 of Rekka no Ken, Nils in a certain chapter of the same game and Duessel in Sacred Stones are good examples) instead they are protected characters that result in game overs if they die.