Harry Potter
Note: list of costumes by year is at the bottom of the page
What got Irvin into cosplay, and what remains the centerpiece of his cosplaying hobby, is Harry Potter. It began in 2008, when Irvin made a stab at Minerva McGonagall for Halloween. A few months later, he joined The Group That Shall Not Be Named (TGTSNBN), which created countless opportunities for HP cosplay, and people with whom to hone the craft. There were annual (or even semiannual) cosplay days, parties, movies releases.
Several years in, Irvin also started attending HP conventions, and quickly realized they are the ideal showcase for all of his best outfits. He will generally try to cram at least two or three outfits into each day, leading to weekends of up to a dozen costumes, a chance to both show off his best stuff and craft new costumes. His best efforts are made at the semiannual conventions in Laconia, NH: Aeternitas 2011, MISTI-Con 2013 / 2015 / 2017 / 2019. But he was no slouch at Leviosa 2016 / 2019 either, despite having to fly there. All told, he has cosplayed 43 of these characters at these conventions - there is a chart of which costume was seen where at the Con Summary page.
Over the years, Irvin has cosplayed over 60 HP characters (not even counting all the Puffs cosplays). Among those are all the Triwizard Champions and Headmasters, most of the Black Family, all of JKR's "Main Seven," a lot of Hogwarts Professors (including all of the DADA ones), and all seven Weasley children. (These notable sets are viewable at the bottom of the page.) He generally cosplays as the book version of characters, though he has done several characters in their A Very Potter Musical iterations.
His costumes have been honored in contests like MuggleNet's Costume Contest and at parties thrown by TGTSNBN and various other HP groups, and have won awards as diverse as Sexiest Costume (Tonks) and Most Festive Costume (Regulus), as well as four different Merlies.
List of HP cosplays, by character's last name.
Portraits
House-Elves
Ghosts
Fantastic Beasts
Tales of Beedle the Bard
Fantastic Beasts and Where to Find Them
A Very Potter Musical/Sequel
Potter Puppet Pals
Original Characters