Dungeon Defenders has many account-wide features rather than character-specific ones. Your characters share a single bank for money and items, and you can pass upgraded items to the next generation. Your tavern o’ achievements is the same for all characters, rather than suggesting that you repeat all the achievements on every character. You unlock levels for your account rather than your characters, so beat the game once to make everything available for all future characters. You probably cannot beat the end boss with your level 1, but the map is there.
One unusual feature is that you can swap characters during the Build Phase of each wave. The tip screen encourages you to combine towers from different heroes, which is a nice synergy bonus for having multiple characters. You can also have a tower-focused character build then a combat-focused character fight through the round. It’s a bit of micro-management, but what are optimizers if not micro-managers? (There are limits here. You cannot have unlimited build time on the highest difficulty, so you are limited by how quickly you can swap characters, run around the map, build, repeat.)
This lets you skip the low levels at which map difficulty scales poorly. My Squire is 40-ish and can clear the first level on Insane difficulty with a half-dozen towers. Start the map, clear the first wave (6 enemies), you now have enough mana to build the first round of defenses. Swap to your new, level 0 character. Watch the defenses clear a couple of waves, bring back the Squire to build the upper-level defenses. Swap back, watch the rest of the round happen. Congratulations, your new character is now level 13 with 40,000 experience points. It feels like an exploit, and the character has no useful equipment, but it does have all its basic tools to play for real rather than fumbling about with minimal mana and one tower.