Urza, Lord High Artificer
Urza, Lord High Artificer is possibly the most powerful unbanned commander in EDH. Due to this EDH Chamber doesn't recommend anyone to build an Urza deck for casual games, as it is very difficult to build a low powered deck with Urza, and still being able to have fun.
Themes for Urza, Lord High Artificer
Combo
Combo decks are control heavy decks, running a heavy amount of card draw or tutors. If the decks get to assemble the combo pieces the game often ends in an infinite combo.
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.