In the game, Little John has the appearance of a Spearman. As a hero, he cannot be converted and can regenerate health. Like other infantry units, he is affected by all upgrades that affect infantry as well as any other bonuses that affect them.
Despite the attack of 7 that is shown in the unit infobox, Little John actually only has 3 base attack in the HD version, just like regular Spearmen. This was fixed in the Definitive Edition.