Ark Innovation ETF (ARKK) wasn't quite an overnight sensation, but it quickly made up for lost time after a relatively quiet beginning in 2014. Portfolio manager Cathie Wood founded Ark Investment Management after successful stints at Capital Group, Jennison Group, Tupelo Capital Management, and AllianceBernstein. Wood and her colleagues look for companies that lead, enable, or benefit from disruptive innovation, an approach to business strategy popularized by Clayton Christensen and his colleagues in the mid-1990s. (Ark's investment strategy is sort of like disruptive innovation on steroids.) The fund started gaining more attention after its 87% runup in 2017, as well as Wood's bullish call on Tesla (TSLA) in 2018. The fund posted a total return of more than 150% in 2020 and garnered about $10 billion in net inflows for the year, plus an additional $5.2 billion in net inflows so far in 2021 (as of Feb. 11). These torrential inflows make the fund--along with several other Ark offerings--one of the fastest-growing funds in the industry.