Lee Jae Jun, also known as Marcus and formerly known as Maru, is a South Korean singer, dancer, former member of C-CLOWN, TREI and TAN and current member of the duo JT & MARCUS and IN A MINUTE. He graduated from Heungdeok High School and is enrolled at Cheongju University.

He made his debut in July 2012 (at the age of 15) as C-CLOWN's lead rapper, lead dancer, vocalist and maknae with their first mini-album, "Not Alone" (using the stage name Maru). The group was managed by Imagine Asia (formerly known as Yedang Entertainment). In October 2015, the agency announced C-CLOWN was disbanding, so he decided to leave the agency. He began using his birth name and, in 2017, switched agencies.

Originally formed as a duo alongside Chae Chang Hyun, he re-debuted in August 2017 as TREI's leader with their digital single "Up". The agency, Banana Culture Entertainment, decided to restructure the group and added a third member in 2018 and re-debuted as a trio in February 2019 with their first mini-album, "Born". Unfortunately, the group was not successful and disbanded in June 2020.

In October 2021, he joined MLD Entertainment and re-debuted once again, now as part of the duo JT & MARCUS (alongside former TREI member Jun Tae or JT) with their first single, "Dear You". They occasionally release a new single and have provided an OST for the drama "Going to You at a Speed of 493 km".

Later that year, he entered the singing survival show "Extreme Debut: Wild Idol" and finished in 5th place, earning a spot in the project group TAN as the main dancer, sub-vocalist and visual. He signed a two-and-a-half-year contract with Think Entertainment and debuted in March 2022 with their first mini-album, "1TAN".

However, the agency became embroiled in several controversies and all members ended their contracts in June 2024. A few weeks later, leader Lee Chang Sun announced the group's disbandment.

He made his acting debut by appearing in the 2023 BL web story "CityBoy Log".

He then re-debuted in October 2024 as part of the trio IN A MINUTE with Kim Jun Tae and Kim Hyun Yeop. They had a fan meeting in Seoul and pre-released the singles "Unbox" and "What You Want".