India has a millennia-long recorded history, with numerous forms of head of state and government. Since 1950, the head of state has been the President, and since 1947 the Head of Government has been the Prime Minister. Governments prior to 1947 were primarily monarchical, with the Monarch of the United Kingdom doubling as Emperor or Empress of India from 1877 until 1947.
The following individuals ruled India during or after the point of divergence of one of Harry Turtledove's alternate history timelines. Most Turtledove PODs occur when India is a part of the British Empire.
Many stories contain references to rulers who died before the POD. Stories set in the history of OTL may reference the incumbent ruler. These do not belong here.
Incumbent at series' end, 1945
Incumbent at novel's end, 1995
(*) Not referenced in novel.
George VI of Britain plays background roles in Worldwar, The War That Came Early, and Joe Steele. In Worldwar, he is Emperor of India until 1944, when the Peace of Cairo cedes India to the Race Colonies on Tosev 3. In The War That Came Early, he remains Emperor at the conclusion of the series, but his position is quite tenuous. In Joe Steele, the British Empire's control of India probably ended as in OTL, but the novel does not address this.
In Through Darkest Europe, India is divided into multiple nation-states. In the mid 20th century, the warlord Faruq al-Ghaznavi seized power over most or all of India, and ruled brutally until his overthrow in a WWII analog. What title he used is unclear.
In Curious Notions, set in 2096, India was never decolonised. As Great Britain is subject to the German Empire, it is unclear whether the Kaiser of Germany or the King of England (both of whom are referenced in broad strokes) is the Emperor of India.
Historical rulers in non-ruling roles
Victoria of Britain is referenced in The Guns of the South and the Atlantis series in her OTL role as Monarch of the United Kingdom. The former work ends before 1877, while it is not known if the title Empress of India exists in the latter series.