Article (website)  (2005)  Page(s) 6.  
 
...he (Paul Ruschpler) released two of the three cultivars of a rosarian named Elze:... and, in 1878 'Kaiser Wilhelm I', a grenadine with violet hybrid perpetual from 1878."

Book  (Jun 1992)  Page(s) 171.  
 
Kaiser Wilhelm I Hybrid Perpetual. Elze/Ruschpler, 1878. The author cites information from different sources... Light purple red... Kaiser Wilhelm I; lived 1979-1888; king of Prussia.

Book  (1936)  Page(s) 758.  
 
Wilhelm I, Kaiser (HP) Ruschpler 1878; fiery purple, shaded light purple and violet, very large, double, .., fine form, doesn't open well, fragrance 5/10, floriferous, repeats, pretty foliage, no prickles, growth 6/10. Sangerhausen

Book  (1880)  Page(s) Annex, p. 67.  
 
hybrid perpetual. Kaiser Wilhelm I. (Dr. Ruschpler, 1878), Blooms fiery purple; pale purple and violet toned, very large, double, very nice and regularly built, fragrant, nice foliage, without thorns.