Main Hero

When you first start the game, you will be asked to name your Main Hero. The main hero is going to be what determines your Base Tap Damage. Every time you tap the monster, it will do your Base Tap Damage plus any Tap Damage Modifiers you may have.

The main hero also has Active Skills that you unlock at levels 50, 100, 200, 300, 400, 500, and 600.

Each skill is on a separate cooldown and can be modified by Artifacts you may have. The arguably most important skill of the main hero is the one you unlock at level 600, Prestige. Prestige is what you use to earn Relics to purchase Artifacts. You will want to use Prestige once you can’t advance through the stages very quickly anymore. The idea is that you will run into walls that can only be passed by obtaining and leveling Artifacts.

Tip: Do not level your Main Hero past level 600. You will receive almost no Tap Damage from leveling them anymore and you get no new skill unlocks.

Purchasable Heroes

Reddit User oLaudix created a great chart for all the purchasable heroes and the base cost for each.

Name Base Cost
Takeda the Blade Assassin 50
Contessa the Torch Wielder 175
Hornetta, Queen of the Valrunes 673.75
Mila the Hammer Stomper 2853.33
Terra the Land Scorcher 1.33E+04
Inquisireaux the Terrible 6.81E+04
Charlotte the Special 3.84E+05
Jordaan, Knight of Mini 2.38E+06
Jukka, Master of Axes 2.38E+07
Milo and Clonk-Clonk 1.43E+08
Macelord the Ruthless 9.43E+08
Gertrude the Goat Rider 6.84E+09
Twitterella the Tweeter 5.47E+10
Master Hawk, Lord of Luft 8.20E+11
Elpha, Wielder of Gems 8.20E+12
Poppy, Daughter of Ceremony 1.64E+14
Skulptor, Protector of Bridges 1.64E+15
Sterling the Enchantor 4.92E+16
Orba the Foreseer 2.46E+18
Remus the Noble Archer 7.38E+19
Mikey the Magician Apprentice 2.44E+21
Peter Pricker the Prickly Poker 2.44E+23
Teeny Tom, Keeper of the Castle 4.87E+25
Deznis the Cleanser 1.95E+28
Hamlette, Painter of Skulls 2.14E+31
Eistor the Banisher 2.36E+36
Flavius and Oinksbjorn 2.59E+46
Chester the Beast Tamer 2.85E+61
Mohacas the Wind Warrior 3.14E+81
Jaqulin the Unknown 3.76E+111

All Purchasable Heroes unlock a passive bonus at levels 10, 25, 50, 100, 200, 400, and 800 with the exception of Eistor the Banisher who unlocks skills at 10, 25, 25, 50, 200, 400, and 800.

Source: WIKI