Swami Sivananda (1887 - 1963)
Swami Sivananda is a very key figure in the sanatana dharma tradition (Hinduism) in the 20th century. As a medical doctor in Malaysia who worked with plantation workers and acutely noticed their sufferings and also his own helplessness to treat anything beyond the physical, he took the Sanyaas route to understand how to alleviate suffering in mankind. His legacy today is marked by the many well known Gurus who founded institutions themselves that have since created a tsunami of all the best things about hinduism worldwide. He has influenced many people directly and indirectly through his writings on all the major Hindu scriptures in plain and simple English. The institution he founded called the Divine Life Society has its motto as Serve, Purify, Love, Meditate and Realize as a path to god.
Some Interesting Links
Autobiography of Swami Sivananda
Sivananda's meeting with great saints
Video of Swami Sivananda