Final answer:
William Wordsworth was an influential British poet early in his career, known for his critical role in the English Romantic poetry movement and for his appointment as Poet Laureate in 1843.
Step-by-step explanation:
The British poet who was highly successful and influential early in his career was William Wordsworth. Wordsworth made significant contributions to English romantic poetry, particularly through the publication of Lyrical Ballads alongside Samuel Taylor Coleridge. This work is often considered a milestone in English Romantic poetry. Wordsworth's legacy includes a treasure trove of poems that encapsulate the Romantic era's spirit, emphasizing the beauty of nature and the inner world of human emotion. Moreover, Wordsworth was appointed Poet Laureate following the footsteps of Robert Southey in 1843, marking him as an influential and recognized poet of his time.