Mages are champions who focus on dealing magic damage by using spells and building ability power items. Mages are typically either high in damage-per-second or high in burst. Mages are often susceptible to being focused in fights and being locked down with crowd-control, but excel at doing the same thing to enemy carries. Mages are most often played in the middle lane and are a ton of fun.
Annie, the Dark Child, is a burst mage that deals massive damage with various fire spells and summoning her massive, fiery teddy bear, Tibbers. Her passive allows every few spells to stun enemies, which when combined with Tibbers, can stun entire teams and deal tons of damage. Annie is very easy to play and is recommended for all new players to learn. With long range, high damage and crowd-control, she has a very safe laning-phase and terrifying team-fight presence. She does everything pretty well, but gets outclassed by other champions that do specific things better. Overall, she is a great mage for beginners and is a lot of fun.
Karthus, the Deathsinger, is an immobile mage that focuses on high damage-per-second within a large area. When focusing only a single target, his damage increases. He also has a unique ability in his ultimate, Requiem, that deals a huge burst of damage to every enemy champion at once. Karthus is not very popular right now because of his severe lack of mobility, but back in the day, he was many player’s go to mage. In addition to a high damage output, he gets seven seconds after death to continue dealing damage without being interrupted or targeted. He may not be super strong in the current meta, but he is still a fun-to-play, iconic champion.
If dealing lots of magic damage and casting spells sounds like fun to you, try playing a mage!
To learn more about another role, check out this guide on supports!