Boros
The Boros combines whites order and justice with reds passion and aggression, creating the legion of Boros. Boros is combat heavy with strong synergies with artifacts, especially equipments.
Boros themes
Artifacts
Artifact decks aim to interact and gain advantage with own artifacts by copying them, turning them into creatures and simply create new artifacts as tokens. Artifact decks are very popular and they have multiple infinite loops.
Lifegain
Lifegain is one of the the most popular themes in EDH. Multiple triggers to gain life and value received from the lifegain triggers are really fun to follow as a player. Often lifegain is combined with another theme, +1/+1 counters or creature tokens, as pure lifegain is often not powerful enough to win the game.
Voltron
Voltron decks focus on commander damage or a few creatures and turns them into massive, protection-from-everything kind of creatures and finishing off the opponents in combat.
Burn
Burn is reds primary mechanics. Red can deal massive amounts of damage to single target or deal multiple amounts of single damage to multiple targets. Burn decks aim to win with massive outbursts of big, uncounterable and unpreventable damage to opponents (and sometimes the burn player itself).