Steve Mandel's firm invests in newly public fintech company. : Lone Pine Capital, the hedge fund founded by Steve Mandel (Trades, Portfolio) in 1997, revealed a stake in Marqeta Inc. (MQ, Financial) earlier this week. The Greenwich, Connecticut-based firm picks stocks using a long-short strategy that focuses on bottom-up, fundamental analysis. Combining growth and value strategies, the firm, whose founder was a former “tiger cub” of Julian Robertson (Trades, Portfolio), is known to not hold positions for very long.