Takeshi Morishima is the largest ROH World Champion to date at 6 ft 3 in (190 cm) and 308 lbs (140 kg)
Low Ki is the smallest ROH World Champion to date at 5 ft 8 in (173 cm) and 180 lbs (82 kg)
Bryan Danielson and Nigel McGuinness have had the most title defenses to date with 39 (33 wins, 2 losses, 3 time limit draws and 1 double disqualification for Danielson and 34 wins, 4 losses and 1 time limit draw for McGuinness)
One of Bryan Danielson's losses was a count out loss to Nigel McGuinness. Since the ROH World Title doesn't change hands on a count out, he kept the title. The other was when he lost the title to Homicide.
McGuinness lost three times by disqualification. This makes him the champion with more disqualification losses to date. The fourth loss was when he dropped the belt to Jerry Lynn.
Only three champions to date have gone to 60 minute time limit draws.
Nigel McGuinness also has gone to a time limit draw that was officially announced as a 60-minutes time limit draw, against Tyler Black. By the way, ROH Wrestling later announced that that was a time keeper's mistake, as the match ended shortly after the 45 minutes mark.
Low Ki, Xavier, Samoa Joe, Austin Aries, James Gibson, Takeshi Morishima and Jerry Lynn all won the title in under one year following their debuts (Low Ki and Xavier both won the title during the first year of Ring of Honor's existence).
Takeshi Morishima holds the record for shortest amount of time in ROH before winning the World Title, winning the title in only his second match in the promotion.
Bryan Danielson is the only person to ever hold the ROH World title while also holding another ROH title (as World Champion he defeated Nigel McGuinness to win, and unify, the ROH Pure Championship on August 12, 2006. On August 25 he officially retired the Pure Title before returning the physical belt back to McGuinness)
To date, Austin Aries holds the record for defending the title in the most countries. Besides defending it in the United States on a regular basis, he also defended in these countries:
Canada: defeating Kevin Steen in Montreal, Quebec in January 22, 2005
Switzerland: defeating Marc Roudin in Weesen, Switzerland on March 12, 2005
Austria: defeating Are$ and Steve Douglas in Krems, Austria on March 13, 2005.