Warwick is a midgame ganker with high sustain and a variety of build paths thanks to his ability to utilize on hit effects with high effieciency thanks to his ultimate applying on hit effects. Warwick also has high chase potential with his Blood Scent, enabling him to finish off low health targets. He is a strong dueling champion thanks to the innate lifesteal in his kit, making one on one fights typically heavily tilted in his favor.
Passive – Eternal Thirst
Warwick's basic attacks deal bonus magic damage and heal him for the same amount.
Q – Hungering Strike
Warwick swipes at the target enemy, dealing magic damage and healing himself for 80% of the damage dealt.
Against enemy champions, Hungering Strike's base damage changes to a percentage of its target's maximum health if it's higher than the flat damage
W – Hunters Call
For 6 seconds, Warwick gains bonus attack speed and grants half of that bonus to all nearby allies
E – Blood Scent
Warwick gains Sight icon sight of all nearby enemy champions with less than 50% of their maximum health, also alerting them to his presence.
While any enemies are revealed this way, Warwick gains bonus movement speed
R – Infinite Duress
Warwick blinks to the front of the target enemy champion and channels for 1.5 seconds, suppressing them for 1.8 seconds and dealing magic damage 5 times in 0.3 intervals. Warwick gains 30% Life Steal for the duration, and each damaging strike applies on-hit effects.
Buy a Banshee's Veil. Aside from the resistances that you'll probably need for any other champions on the enemy team, it also forces him to walk up and break the spell shield before he can ult you successfully
Warwick can't gank effectively before level 6, you can use this time to snowball lanes as the jungler, or pressure your enemy laner
Quicksilver Sash removes the supression from Warwicks ultimate, you can use this to make yourself an invalid target
Buying/Taking anything with grevious wounds such as ignite or Mortal Reminder makes Warwicks life hard as it reduces his ability to regenerate health
She's basically just WW but better. Minus the easily remedied CC that Warwick offers. She scales hard and can gank at level 3. Not hyper effectively, but better than Warwick. Also, she doesn't mind farming up like him, and has a larger teamfight presence with her ability to peel WW off of a carry with her own ult
Zac just makes Warwicks life bad. He has high base damages and can stop Warwicks ult with the two built in knockups he has. He's better at engaging teamfights and can snowball the lanes at level 3+.
He can cancel WW's ult really easily, and get him killed with his high amount of CC. He can gank at 3, and can survive a 1v1 against WW for a long time when built as a tank. Gragas is a peeling machine, but his clear speed is a little worse with the recent nerfs. Definitely a pick to specifically counter a champion
Itemization comes easily against Warwick. QSS, Mikaels, Banshees Veil along with the hard CC that every team should have should totally invalidate Warwick, since the only thing he really offers his team one form of hard CC and a little damage. It's also worth building a Morellonomicon and Mortal Reminder to counter any healing he seeks to do