I've posted him a few times already, but this souns like a good place to re-post:

The Eldritch Blast Knight

VHuman fighter (eldritch Knight) 7 Warlock (Infernal/Tome) 13

An unconventional gish build. Switch seemlessly from long range to melee range, push your enemies around into hazards or away from your squishies. With quick access to 3rd level slots, you get access to a good range of spells for decent area attacks (fireball) or control (Hunger of hadar) or movement (misty step/fly), even maybe counterspelling depending on your need. Action surge at level 7 gives you some nova potential, and hex with a great concentration check makes for some very decent sustained damage potential. Heavy armor and shield, coupled with thp on kil;s and decent hit dice, means you are not going down easy and can tank with the best of them. Access to all ritual spells and a familiar make you usefull outside of combat, and a high charisma score means you can be a decent party face.

15 Str /10 Dex /14 Con /8 Int / 10 Wis / Cha 16

Lvl 1: Vhuman Fighter 1 (feat: crossbow expert) (defense fighting style)
Lvl 2-6: Warlock (Fiend) (Tome) Pick up Eldritch blast with repelling and Agonizing blast, grab Booming blade and Shillelagh cantrip. Grab Warcaster for your ASI.
Lvl 7-12: Fighter (Eldritch knight). Max Charisma with the ASIs.
13-15: more warlock.

At level 5: You are Fighter 1 Warlock 4.
You are wearing heavy armor and shield with defense style, 21 AC with plate and 40 HP. On a kill you get 7 thp, and bonus action heal for 1d10+1 means you are fairly self sufficient for HP and can take tanking duty.
You cast Eldritch blast in melee and at range as you want, for a very stable 2d10 +6 damage per turn. The cool feature here is you can use this to push enemies 20 ft away where you want. Being in melee makes controlling the angle of the pushing quite easy, and adds a tactical layer regular fighters don't have.
You have proficiency in concentration (so +5) and advantage on those check, so you can maintain hex no problem. Next level you get third level slots, so that Hex can last 8 hour.
You have two 2nd level spell slot which recharge on a short rest.
For attack of opportunity, Booming blade delivered through you shillelagh is the key (2d8+3 and another 2d8 from the secondary). Pre-cast shillelagh anytime you think a fight might break out in the next minute, as you've got competition for that bonus action with Hex.
You might also burn a slot on Hellish rebuke if you fancy it.
Sample spell list: Hex, Hellish rebuke, Armor of aghatys, Misty step
Cantrips: Eldritch Blast, Booming Blade, Prestidigitation, Minor Illusion, Guidance, Shillelagh.

At level 11:
You are Warlock 5 Fighter 6.
Your Charisma is now maxed.
Your AC is still at least 21, and you got Shield 3 first level slot per day to raise it to 26 when needed (or to cast Absorb elements). HP is at a respectable 87, with THP on kills of 10. You can heal 1d10 + 6 as a bonus action. You can take tanking duty no problem.

Eldritch blast is now at 3d10 + 15, which is pretty great at-will damage with a push rider of 10 feet per attack. With Hex, 3d10 + 15 + 3d6. But you also have Action surge and up to 8 hour of Hex with a single cast. So you got a once a short rest nova of 6d10+30+6d6 with 60 feet of potential pushing. That is pretty brutal and useable both in melee and at range.

Your fifth warlock level came with an extra invocation, so you need to choose: Devil sight opens the Darkness shenanigan, Book of ancient secrets gives you access to nearly all rituals in the game (including a familiar), or at-will silent image or disguise self... you decide, but you've got quite a few choice, depending on your party to open up your usefulness.
Sample spell list: Hex, Hellish rebuke, Armor of aghatys, Misty step, Fireball, Shield, Absorb element, Magic missile, protection from evil and good.
Cantrips: Eldritch Blast, Booming Blade, Prestidigitation, Minor Illusion, Guidance, Shillelagh, Mage Hand, Message.

Level 12 you get two level 2 spell slots and War magic. Why? To use your staff to attack the enemy once more after casting eldritch blast, and trigger Hex one more time! So now, your at-will damage is 3d10+15 +1d8 +5 (with shillelagh active). You do have a bit of competition for bonus action, so it,s not gonna come toghether perfectly all the time.

At level 18
You are Warlock 11 Fighter 7.
On top of all the above, if you now have your fourth blast, so the fighter is jealous he's got less attack than you.

You have 3 level 5 spell slot that recharge on a short rest, 4 level 1 slot and 2 level 2 slots on long rest, and a 6th level spel with your Mystic arcanum. The ranger, paladin and eldritch knight are super jealous at your spellpower, and your at-will damage (4d10+20 + 1d8+5) is more than a match to theirs, and your short rest nova (8d10+40 + 8d6) is nothing to sneeze at. Hex is now 24 hours long.

5 invocations gives you some versatility.

Sample spell list: Hex, Hellish rebuke, Armor of aghatys, Misty step, Fireball, Counterspell, Fly, Shadow of Moil, Firewall, Hold monster, Synaptic Static, Soul cage (Arcanum)
From Eldritch knight: Shield, Absorb element, Magic missile, Protection from evil and good, Darkness
Cantrips: Eldritch Blast, Booming Blade, Prestidigitation, Minor Illusion, Guidance, Shillelagh, Mage Hand, Message, Chill touch

On your next two level, you get a 7th level spell