Harold Eugene Clark was an American singer-songwriter and founding member of the folk rock band the Byrds. He was the Byrds' principal songwriter between 1964 and early 1966, writing most of the band's best-known originals from this period, including "I'll Feel a Whole Lot Better", "She Don't Care About Time", "Eight Miles High" and "Set You Free This Time". Although he did not achieve commercial success as a solo artist, Clark was in the vanguard of popular music during much of his career, prefiguring developments in such disparate subgenres as psychedelic rock, baroque pop, newgrass, country rock, and alternative country. He was inducted into the Rock and Roll Hall of Fame in 1991 as a member of the Byrds.

The Byrds were an American rock band formed in Los Angeles, California, in 1964. The band underwent multiple lineup changes throughout its existence, with frontman Roger McGuinn remaining the sole consistent member. Although their time as one of the most popular groups in the world only lasted for a short period in the mid-1960s, the Byrds are considered by critics to be among the most influential rock acts of their era. Their signature blend of clear harmony singing and McGuinn's jangly 12-string Rickenbacker guitar was "absorbed into the vocabulary of rock" and has continued to be influential.