= new reply since forum marked as read
gmta. 
German warmbloods are named with the 1st initial of their father's name. In this way, they have produced several "lines" of warmbloods with recognizable characteristics. It is a marketing technique, and has been a very successful one. For example, I knew immediately that Ann's famous fraud involving Super Hit was a horse tracing back to the famous Sandro Hit.
Over time, they run out of names, so sometimes just make things up. Maybe it's a combination of father's and mother's name. Who knows? 
The "R" lines trace back to the stallion Rubenstein. They are known for calmer temperaments that are good for adult amateurs, with gaits and talent to satisfy their professional trainers. They tend to be late developers, with very good canters, but their trot takes time to bring out.
A former Olympian and American, Lisa Wilcox, works for a major German breeder riding his "R" line stallions. She rode in the Olympics on Rohdiamont (red diamond). (She is, by the way, Ebeling's ex. She preferred to stay in Germany and train with the best. Ended up employed by a top German breeder and beat her ex to the Olympics).
The leading rider representing the US in this Olympics is the German Stefan Peters, on another "R" line stallion, Ravel (no translation needed here, lol).
Other popular lines are the "B" line (traces back to the arabian Bolero. they like to mix some t-bred or arab in, but prefer their "blood" at F5); the "W" line (the Hanoverian World Cup, usually through Weltmeyer or Warkant); the "D" line (traces to the Hanoverian Donnerhall); the "F" line (traces to Wendekreis, but they switched his line to "F" to differentiate from "W." The W's are dressage specialists; the F's are generalists.
Note that the European warmbloods are not breeds, but registries. They have an approval system based on quality; not all of their horses are approved for breeding and eligible for registry. Except for the the Trakehners, which are a true breed, they are a mix of native draft, trakehners, arabians, and t-breds that has been refined over many generations through their standardized breeding program. Each region has its own registries; thus the Oldenburgs, Hanoverians, Holsteiners, etc. Cross-approvals happen all the time. And the Dutch Warmblood Society jumped the pack into its race with Germany to dominate dressage by crossing a lot of German Warmbloods into their native horses.
