Btw, could you define "Core Only". I'm taking that to mean the first book only, but different GMs have different definitions of Core.

If you want to go with a Charger, and keeping Core only in mind, I'd probably suggest a Halfling Paladin. This gives you a tough full BAB Chasis and you can pick up a mount with your Divine Bond at level 5. This'll mean levels 3 and 4 will be on foot, unless you buy a mount know and pick it as your Bond once you level up.

If you have a decent enough Point Buy for 16 Strength, you'll charge for 2d6+6 with a Lance. Unfortunately most of the best feats for a mounted charging build come from other sources. You will have the benefit of being able to stay mounted even in dungeons though.

Alternatively, a Dwarven Druid could be excellent for providing ways to handle large numbers of enemies. First, pick an animal companion with plenty of attacks. Large Cats (Lion, Tiger, ect) are a favorite due to having Pounce and 3 Natural Attacks. This lets them charge and get a full attack in each round. Pump up your Druid's wisdom and you can use crowd control and AOE spells to help take down large groups too. Remember that when you face huge numbers, the monsters aren't usually very strong (individually). I've seen Entangle used too good effect in that situation, and as a first level spell you'll have it right out of the gate.