Complex sentence: In the early years of the Grateful Dead, McKernan became a minor celebrity due to his distinctive biker image, to the extent that in 1969, the band's record company, Warner Bros. Records ran a "Pigpen Look-Alike Contest".
Split into simpler sentences: In the early years of the Grateful Dead, McKernan was easily recognisable by his biker image, making him a minor celebrity. In 1969, the band's record company, Warner Bros. Records ran a "Pigpen Look-Alike Contest".