The correct answers are the last two:
a statesman named Solon who made laws prohibited the enslavement of debtors;
and
the leadership of Cleisthenes who presented a constitution in 508.
Solon (640-558 BC) did not originate democracy in Athens, but did take steps that led in that direction. According to the American School of Classical Studies at Athens, "While Solonian reforms did not establish democracy, they were a crucial step on the Athenian road to democracy. Solon's constitution, consisting of moderate redistribution rather than a revolutionary transfer of political power, nonetheless granted important rights to the lowest class of citizens."
Cleisthenes (570-508 BC) is known as the founder of Greek democracy. He aligned himself with the Assembly (of the people) against the aristocracy and managed to impose democratic reforms by means of a new constitution that was approved by the Assembly and implemented in 508 BC. There's much more to the story than that, but we'll keep it brief here.
As to the other answers, Plato founded a school of thought in Athens prior to Aristotle, and neither of them viewed democracy all that favorably.
Nobles worked against tyrannical monarchs for their own benefit, not to spur democracy.
Tyrants were called "tyrants" (a word referring to an absolute ruler or dictator) because they ruled for their own interests, not for "the needy."
Oligarchy ("government by the few") would not support democracy ("government by the people").
