Galio

In my opinion, Galio is probably one of the most underplayed tanks in the game. He can take a hit, and his passive allows him to be defensive while also being able to deal damage. his ultimate can also taunt enemies into attacking him, effectively holding them in place for his allies while taking half the damage he would be otherwise. at the end of it, he deals a good amount of damage to them himself.

Galio's passive gives bonus AP, determined as 50% of his magic resistance. this allows him to be tanky while  still being able to deal damage.

His Q shoots a blast of energy in a targeted circle. anything that's in this circle takes full damage and is slowed (% depending on level of ability). This ability, along with his E, are great for harassing pre-fighting and then chasing down an enemy later.

E creates a shield for an ally (or himself) for four seconds, that increases their armor and magic resist. every time the ally with the shield takes damage, Galio is healed a bit of health. This is a great ability for soloing minion waves with reinforcements still a bit behind. If the ally takes consecutive hits from the same enemy, the healing to Galio is reduced by 20%.

Galio's E shoots a gust of wind in a path. Any enemy in the path takes damage. The gust of wind leaves a trail in a straight line behind it. any allies that walk on the trail have their movement speed increased. This also helps when chasing down an enemy.

His ultimate ability turns Galio into a statue. He can not move or do anything while in this state. While his ultimate is active, enemies in the circle are taunted into attacking him and can not leave until it is over. He takes 50% less damage while in this state. every attack Galio takes, he deals 5% extra damage up to 40%. This may give incentive to use his ultimate while in a wave of minions to take some extra hits. He can also hold champions with his taunt while the rest of your team deals damage to them.

I could really get into playing as Galio. I always enjoy a good AP tank. Honestly I think the reason more people don't play as him is because of the fact he's a support. I really don't understand why people don't like to play supports, but whatever.