I see, I'll try to make a list with a quick explanation on those kind of champs, you can look out for pro players playing them in solo queue in youtube have a little more in depth:
Dr Mundo, he is melee, but most of the damage comes from his cleavers (Q) which have a low cooldown, he is not a big damage dealer but is probably the tankiest champion in the late game (~over 40 minutes of a game)
Cho'Gath, these days he is played more in a mage role in the midlane, but he can be played in a way more tank oriented way, he is melee, but his Q has big range (AoE knock up), also his W's range is decent(AoE silence).
Galio, Melee mage, with a nice shield which heals you when you take damage, you'll be using your Q and your E most of the time to trade, you can go full tank to full ap on him, fun to play, and its ult is great for teamfights!
Gragas, melee offtank mage, maybe not what you are looking for, but he can waveclear and poke nicely through his Q
Gnar (i think this may be the one you are looking for), he has two forms, gnar, where he is a ranged AD champ, and by attacking and landing his boomerang (Q), gains rage, at 100 rage you become mega-gnar, in this form you move slower, you lose range and become melee, but you deal aoe physical damage and you gain bonus health, armor and magic resist. The big con of playing him is that is hard to manage your rage to turn into mega gnar in the correct moment (right at the start of a teamfight for example).
Nasus (I love this one), you dont have poke or range, but you have your passive which lets you sustain through the damage you take, the main thing about playing nasus is farming your Q, it gives you free damage just for last hitting minions or monsters with it, so you get just one damage item (trinity force) and then proceed to build full tank, if you stacked your Q well, you can be in the middle of a teamfight being the tank and doing massive amounts of damage.
Urgot, low range, can be built full glass cannon or offtank, your ultimate gives you defensive stats that help you a lot surviving teamfights.
Sorry about my english bro!, hope it helps, if you have any other question feel free to ask!