Lyndon B. Johnson was the 36th President of the United States, serving from 1963 to 1969. He took office after the assassination of John F. Kennedy and is known for his ambitious domestic agenda called the "Great Society." This program aimed to eliminate poverty and racial injustice, leading to significant reforms in education, healthcare, and civil rights. Johnson also escalated U.S. involvement in the Vietnam War, which became a controversial aspect of his presidency. Despite his domestic achievements, the war led to widespread protests and criticism, ultimately affecting his decision not to seek re-election in 1968.