Ron \Pigpen\" McKernan"

Context: Along with Garcia and second guitarist Bob Weir, McKernan was a participant in the predecessor groups leading to the formation of the Grateful Dead, beginning with the Zodiacs and Mother McCree's Uptown Jug Champions. Drummer Bill Kreutzmann was added and the band evolved into the Warlocks. Around 1965, McKernan urged the rest of the Warlocks to switch to electric instruments. Bassist Phil Lesh joined soon after, and they became the Grateful Dead. The group were keen to involve McKernan in the band, as he was the group's original leader and was considered the best singer and frontman.  The Dead's early sets centered around blues and R&B covers chosen by McKernan. By the end of 1966, Garcia had improved his musical skills and wanted to assert himself more as a leader and musical director, changing the band's direction and reducing McKernan's contributions. In 1967, drummer Mickey Hart joined the Grateful Dead, followed by classically trained keyboardist Tom Constanten in 1968, further changing the group's style. Constanten often replaced McKernan on keyboards in the studio, as McKernan found it difficult to adapt to the new material that Garcia and Lesh composed for the band.  In October 1968, McKernan and Weir were nearly fired from the band after Garcia and Lesh believed their playing was holding the band back from lengthy and experimental jamming. Garcia delegated the task of firing them to Rock Scully, who said that McKernan "took it hard." Weir promised to improve, but McKernan was more stubborn. According to Garcia biographer Blair Jackson, McKernan missed three Dead shows before vowing not to "be lazy" any more and rejoining, while Kreutzmann objected to replacing McKernan and said the event never happened. Following his discharge from the United States Air Force in November 1968, Constanten officially joined the band, having only worked in the studio while on leave up to that point. Road manager Jon McIntire commented that "Pigpen was relegated to the congas at that point and it was really humiliating and he was really hurt, but he couldn't show it, couldn't talk about it." He began to take Hammond organ lessons and learned how to use the various drawbars and controls.  After Constanten's departure in January 1970 over musical and lifestyle differences, McKernan nominally resumed keyboard duties. He contributed instrumentation to only two tracks (Hammond organ on "Black Peter" and harmonica on "Easy Wind", the latter as lead vocalist) on Workingman's Dead (1970), the band's breakthrough studio release. On the follow-up album American Beauty, keyboard parts were handled by Garcia and Lesh, along with session musicians Howard Wales and Ned Lagin. The 1971 live album Grateful Dead featured three overdubbed organ parts from Merl Saunders in addition to McKernan's contributions on "Big Railroad Blues", "The Other One", and "Me & Bobby McGee". While Garcia expressed frustration at McKernan's missed rehearsals and his inability to keep up with new material, Lesh was more forgiving, opining that "it was okay for Pigpen to lay out... we kept wanting Pigpen to be there because he was 'one of us.'" CANNOTANSWER

Question: what happened in 1966 to the Grateful Dead?
Answer: the end of 1966, Garcia had improved his musical skills and wanted to assert himself more as a leader and musical director,