Ross Perot won 8 and 18 percent of the popular vote over the course of two federal elections. Since then the most any third candidate has received is about 3%, and going back nothing comes close until someone won 6% in the 1980 election. What made Perot so successful?
In one sense, Perot's candidacy can be seen as the beginning of the sort of "grassroots populism" and anti-establishment sentiment that culminated in the election of Trump in 2016. But there were also factors specific to both elections:
In 1991, GHW Bush was riding high on the back of Gulf War 1 sentiment, and was seen as a very strong front-runner for re-election. This meant that several high-profile Democrats did not make a serious effort to run, and at the time Bill Clinton was not a particularly well-known candidate. To the extent that he was known, it was for his disastrous long-winded speech at the Democratic convention in 1988. The Democrats had also been hurt by a series of candidates that were seen as underwhelming and too left wing (Mondale in 1984, and Dukakis in 1988).
At the same time, the Republicans were deeply discredited on economic matters for the economic recession, and for Bush breaking his promise on "No New Taxes". Once the Gulf War died down and the focus returned to domestic matters, these economic issues began to bite very hard.
So you had a situation where neither side had popular candidates, and both parties carried significant political baggage from the past. Perot positioned himself much as Trump did, as the maverick outsider who would sweep away the "corrupt" and "incompetent" Beltway machine of both parties. In the climate of 1992, this was very attractive.
In 1996, the Republicans ran Bob Dole, a 73 year old who looked every bit of his age. Dole was a competent enough politician, but he was absolutely not the type to energise the base the way that an Obama or a Trump did. There was also some residual dislike for Congress in general, due to the government shutdown of 1995-96, and the fact that both sides were seen to have 'sold out' due to Clinton compromising with Republicans over various issues through 1994-96.
Once again, Perot filled the anti-establishment "plague on both your houses" role, as well as providing a spark and energy to what was seen as a very boring and predictable election.