Untouchable Fighter/Wizard/Cleric (5e Optimized Character Build)
From D&D Wiki
Pick variant human to gain access to the warcaster feat.
If you can, get some adamantine plate. After that, try to find some more defensive items.
Take a level in Cleric, for spells take inflict wounds and shield of faith, use your blessing of the forge to upgrade your shield turning it +1, with this you should be able to manage until higher levels.
Take a level in wizard, and pick up the shield.
Take a level in wizard, and choose the divination school for those d20s.
Take a level in wizard, and learn the mirror image spell, rest is up to you.
Take a level in wizard.
Take the next five levels in fighter. Pick the defense fighting style, and the samurai archetype for extra hp.
When in combat, use your action surge, cast blink and haste, attack right after, you have a 50% chance of disappearing, and you should have 24 AC. If someone attacks you, use the shield spell, now you have 29 AC until your next turn and if someone crits, it does normal damage because adamantine plate. Next turn you cast mirror image, attack, then have a 50% chance to disappear, cast shield if attacked and if your enemy somehow hits you, they have a 50% chance of missing you because of mirror image. Continue attacking, (which you get three of a turn), burn your first level spell slots and then move onto second.