I'm playing through Dragon Age: Origins again with this specific goal in mind, so I'll outline what I've done:
Overview
I've found letting Alistair run on auto-pilot works really well. The aggressive behavior, combined with the tactics loadout described below, makes the AI pretty smart and hands-off. However, you really need to make sure you have a good Spirit Healer (like Wynne) backing him up.
So I've built him around me not having to do anything with him: prioritizing his tactics load-out and passive skills.
Build
Obviously, Alistair is going to be a warrior. You're locked in with the relatively useless Templar specialization, but once you reach 14 and can choose a second, definitely pick Champion.
- Class: Warrior
- Specializations: Templar, then Champion
- Attribute priority: Strength. Pop a couple points into Dexterity when talents require it. If you've built your healer well, you don't need to get fancy with Constitution and Willpower.
- Skills: Combat Training and Combat Tactics; don't bother with the rest. Alternate between selecting the two based on what talents you're about to pick up. If you need a talent that requires the next level of Combat Training get that, otherwise, get Combat Tactics.
- Talents: Concentrate on filling out the tactics load-out described below. Getting to the third tier of the first line of Warrior Talents and all the lines of Weapon and Shield talents should occupy most of your time.
Leveling Priority
Alistair starts with:
- Talents: Righteous Strike, Powerful, Shield Bash, Shield Pummel, Shield Block, Shield Cover
- Skills: Expert Combat Training
I then chose the following as I leveled:
- Shield Defense (Weapon and Shield, 2nd line, tier 1)
- Shield Balance (Weapon and Shield, 2nd line, tier 2)
- Shield Wall (Weapon and Shield, 2nd line, tier 3)
- Threaten (Warrior, 1st line, tier 2)
- Precise Striking (Warrior, 2nd line, tier 1)
- Taunt (Warrior, 2nd line, tier 2)
- Overpower (Weapon and Shield, 1st line, tier 3)
- Bravery (Warrior, 1st line, tier 3)
- Shield Tactics (Weapon and Shield, 3rd line, tier 3, needs 20 Dexterity)
- Shield Mastery (Weapon and Shield, 3rd line, tier 4, needs 26 Dexterity)
- Specialize in Champion to get War Cry
- Death Blow (Warrior, 1st line, tier 4)
- Shield Expertise (Weapon and Shield, 2nd line, tier 4)
- Rally (Champion, tier 2)
- Motivate (Champion, tier 3)
- Superiority (Champion, tier 4)
This should take you to level 20-ish. Note you don't need Master Combat Training until you get Shield Mastery, so spend your skill points on Combat Tactics to make sure you can use your abilities.
Tactics
As mentioned above, I didn't want to micromanage Alistair, so I used the following to handle pretty much every encounter. Note because of my reliance on a dedicated healer, Alistair does not use any sustainability/survival abilities.
- Self: Any → Activate mode: Threaten
- Self: Being attacked by a melee attack → Activate mode: Shield Wall
- Self: Being attakced by a ranged attack → Activate mode: Shield Cover
- Enemy: Nearest Visible → Use ability: Shield Pummel
- Self: Surrounded by at least two enemies → Use ability: Taunt
- Self: Surrounded by at least three enemies → Use ability: War Cry
- Enemy: Health >= 75% → Use ability: Shield Bash
- Enemy: Health < 75% → Use ability: Overpower
Equipment
Equipment choice is not particularly difficult, and I've found you don't need to worry about min/maxing to make him effective, so I'm not going to bother with a mostly unnecessary list of exact gear you need to have. Generally:
- Armor: Equip the heaviest you can find: ultimately, you'll be wearing massive armor. Favor equipment that has stamina regeneration and secondarily, on "tanking" stats like Constitution, Resistances, Armor, etc.
- Weapons: Sword and board: long swords and the largest shield you can find.
Final Thoughts
It's really hard to unintentionally mess up building Alistair: there are so few "tanking" choices in the game that you'll eventually get everything you need by level 15-ish anyway.
Ultimately, it comes either micromanaging Alistair as your de-facto main (which takes practice), or a decent tactics load out (specified above) if that's not your thing.
Finally, I can't stress enough how much a sword and board tank like Alistair needs a good healer. If you're not interested in giving up a slot for a dedicated healer, it's going to be very difficult to keep Alistair effective.
Acknowledgements
The above is an amalgamation of various different guides I've found, notably:
I've confirmed the viability and effectiveness of this advice by using it myself.
Best Answer
Yes, this should work just fine. When I did this on the Xbox 360, I just used the disc to install the DLC from the Ultimate Edition and then still played the digital copy on my hard drive.