Step 1: Note the approximate period of each poet: Kabir – 15th century (c. 1398–1518); Tulsidas – 16th century (c. 1532–1623); Bihari – 17th century (c. 1595–1664); Bharatendu Harishchandra – 19th century (1850–1885). Step 2: Arrange in order of time: Kabir → Tulsidas → Bihari → Bharatendu. Step 3: The earliest is Kabir. Memory trick: Bhakti kaal (Kabir, Tulsi) comes before Riti kaal (Bihari) and Adhunik kaal (Bharatendu). Answer: Kabir.