Given this reference text about the Grateful Dead, tell me who their keyboard players were over the years.

Context: The Grateful Dead was founded in the San Francisco Bay Area amid the rise of the counterculture of the 1960s. The founding members were Jerry Garcia, Bob Weir, Ron "Pigpen" McKernan, Phil Lesh, and Bill Kreutzmann. Members of the Grateful Dead, originally known as the Warlocks, had played together in various Bay Area ensembles, including the traditional jug band Mother McCree's Uptown Jug Champions. Lesh was the last member to join the Warlocks before they changed their name to the Grateful Dead; replacing Dana Morgan Jr., who had played bass for a few gigs. Drummer Mickey Hart and non-performing lyricist Robert Hunter joined in 1967. With the exception of McKernan, who died in 1973, and Hart, who took time off from 1971 to 1974, the core of the band stayed together for its entire 30-year history. The other official members of the band are Tom Constanten, John Perry Barlow, Keith Godchaux, Donna Godchaux, Brent Mydland, and Vince Welnick. Bruce Hornsby was a touring member from 1990 to 1992, as well as a guest with the band on occasion before and after the tours.

Answer: Ron "Pigpen" McKernan was the original keyboard player of the Grateful Dead. Others to play keyboards for the Grateful Dead include Tom Constanten, Keith Godchaux, Brent Mydland and Vince Welnick.