Probationary member and associate as of Avengers (1st series) #137. Accepted full membership in #151.
Beast created a mutagen that accelerated his mutation in Amazing Adventures (2nd series) #11, creating his first gray furred form, stabilizing as blue furred in #14. Years later, Carl Maddicks' retromutagen eradicated Beast's animal features in X-Factor (1st series) #3. After a series of bio-chemical influences and changes, McCoy stabilized as blue furred again in #33.
Beast experienced a secondary mutation after Sage jumpstarted his healing powers in X-Treme X-Men (1st series) #3, leading to the cat-like appearance he first showed in New X-Men (1st series) #114. This remained stabile for years until the onset of another mutation changed his appearance in All-New X-Men (1st series) #1-5.